For the past few days, I’ve noticed some strange behavior in Windows 11 File Explorer. As the day goes on, it becomes increasingly sluggish and sometimes takes up to 30 seconds to display the save dialog.
The reason I’m writing this is that, at the same time, the NextCloud client (33.0.2) is generating a huge number of log entries (every minute a new gz file with 20-200KB). It seems that the following entries keep repeating themselves:
2026-04-15 08:13:54:927 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:475 ]: Desktop client process id: 2652
2026-04-15 08:13:54:927 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:477 ]: Open file completed by process id: 15448
2026-04-15 08:13:54:927 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:478 ]: Open file completed by application id: "UNKNOWN"
2026-04-15 08:13:54:941 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:634 ]: Desktop client process id: 2652
2026-04-15 08:13:54:941 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:636 ]: Close file completion by process id: 15448
2026-04-15 08:13:54:941 [ info nextcloud.sync.vfs.cfapi.wrapper C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\vfs\cfapi\cfapiwrapper.cpp:637 ]: Close file completion by application id: "UNKNOWN"
But I’m not sure now whether this is a bug in the NexCloud client that I should report, or just a symptom of an Explorer issue.
I had searched for relevant posts here on the forum and on GitHub, but only found very old posts that have nothing to do with the current setups.
I wasn’t aware that I could also file an official bug report here. I had initially just hoped to get some guidance from the forum on whether I should submit a full bug report here for the project on GitHub or as an Explorer issue with Microsoft.
I’ll gather the necessary information when I have a moment and fill out the bug report on GitHub.
ummm full bug reports are to be filed on GH, of course.
But sometimes it’s just a setup problem or something similar. so you could try your luck here on the forum.
but without knowing anything about your setup it’ll be very unlikely that someone on here COULD solve your problem. That’s why I asked you for more details.
I know that there is/was a thread about windows client being sluggish sometimes here on the forum. but as far as I remember it was kind of “solved” with a GH-issue (meaning there’s probably nothing the forum could do about).
If a problem only appears every now and then it’s really problematic to track it down to the source of it. even less so if everyone seems to omits more infos about the problematic systems/softwarerversions…
Sorry for the delay in getting back to this. I’m now pretty sure it’s a Nextcloud client issue. More on that below. I’ll provide the basic details about the client computer in additon here. There are no relevant log entries on the server for that time period. Let me know if you’d still like me to post the server logs here.
The Basics
Nextcloud Server version (e.g., 29.x.x): 33.0.2
Nextcloud Client version: 33.0.2
Operating system and version (e.g., Ubuntu 24.04): Linux 6.12.74+deb13+1-amd64 x86_64
Client System: Windows 11 Pro 25H2
Web server and version (e.g, Apache 2.4.25): Apache 2.4.66
Reverse proxy and version _(e.g. nginx 1.27.2): No reverse proxy was configured at the time of the first occurrence
PHP version (e.g, 8.3): 8.4
Is this the first time you’ve seen this error? (Yes / No): For about two weeks
When did this problem seem to first start?: After update to Client 33.0.2
Installation method (e.g. AIO, NCP, Bare Metal/Archive, etc.): Bare Metal
Are you using Cloudflare, mod_security, or similar? (Yes / No) :No
Summary of the issue you are facing:
Windows Explorer seems to freeze regularly for extended periods (up to 30 seconds) of time when saving or moving files, with Client 33.0.x (with support for virtual files).
The freezing doesn’t happen every time, but only once every 5 minutes, up to a maximum of about once per minute.
Since my first post, I’ve been testing a few changes to try to narrow down the problem a bit more. At the same time, there appears to be a correlation with the creation of client log files larger than 200 KB, when the Explorer freeze. I downgraded the client to 4.0.8 as a test. Everything is running more smoothly again (at least as expected from Windows 11). Large log files have also become much less common. In fact, they only appear when the client starts up.
At the same time, there’s a PC running Windows 10 with Client 33.0.2 right next to me. So far, I haven’t noticed any large log files or freezes in Windows Explorer on this machine (same folder, without support for virtual files). The folder structure is quite large (850 GB) and contains a large number of files.
Steps to replicate it (hint: details matter!):
Frequently saving files (Word, Firefox) or moving files in Windows 11 Explorer
Log entries
Nextcloud Client
There are no relevant log entries on the server for that time period. Let me know if you’d still like me to post the server logs here. In particular, the large client log files are full of the following entries.
2026-04-24 14:49:21:429 [ info nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1269 ]: ls col job "FOLDER" new file "/nextcloud/remote.php/dav/files/USER/FOLDER/FILENAME1" 13
2026-04-24 14:49:21:429 [ warning nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1277 ]: skip existing item "FOLDER/FILENAME1"
2026-04-24 14:49:21:429 [ info nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1269 ]: ls col job "FOLDER" new file "/nextcloud/remote.php/dav/files/USER/FOLDER/FILENAME2" 13
2026-04-24 14:49:21:429 [ warning nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1277 ]: skip existing item "FOLDER/FILENAME2"
2026-04-24 14:49:21:429 [ info nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1269 ]: ls col job "FOLDER" new file "/nextcloud/remote.php/dav/files/USER/FOLDER/FILENAME3" 13
2026-04-24 14:49:21:429 [ warning nextcloud.sync.account C:\Users\User\AppData\Local\Temp\windows-38496\client-building\desktop\src\libsync\account.cpp:1277 ]: skip existing item "FOLDER/FILENAME3"
...
Quick update:
I’m now pretty sure this is an issue with the 33.0.x client. I’ve tested versions 33.0.2, 33.0.3, and 33.0.4. In between, I always downgraded to 4.0.8. With the 33.0.x version, these massive lags occur, and they disappear again after the downgrade.
The logs don’t really reveal the cause of the problem. I have the feeling that the lags often coincide with the log file change, based on the timestamps.
I’d actually like to share the log files, but unfortunately, I’m bound by confidentiality regarding most of the paths and other details.