Upload of large files via Desktop client doesn't work

Nextcloud version 11
Operating system and version Armbian/Debian Jessie 3.4.112-sun8i
Device: OrangePiPlus 2E (armhf), 32bit
Nginx version: 1.6.2
PHP version 7
Database: MariaDB
Is this the first time you’ve seen this error and can you replicate it?: Yes

I have the problem, that larger (i think > 50 MB) files cannot get uploaded to my nextcloud server via my Windows Nextcloud Client, but when i upload directly via the website it works! I use a USB storage stick with 128GB as nextcloud storage, which is formatted as exfat and mounted under /media/sdcard5.
With smaller files synchronizing works! Maybe it’s a caching error? Does anyone have an idea?

The output of your Nextcloud log in Admin > Logging:
There are coming two error messages, the first:

fopen(/media/sdcard5/jan/cache/filename.mp4-chunking-765992384-0.HqC1AM5hTJiqQ1ge.part): failed to open stream: Input/output error at /var/www/5/nextcloud/lib/private/Files/Storage/Local.php#287

the second:

Sabre\DAV\Exception\BadRequest: HTTP/1.1 400 expected filesize 10000000 got 0

Can you run a check disk on the usb stick? I/O error are most likely bad sectors.

ok, i ran the

fsck /dev/sda1

on the usb stick (sdcard inside of an usb-to-sdxc-adaptor) an it found 21000 errors!!! That it hasn’s something to do with caching but with the “USB-stick” is the fact, that now the error already occurs at files > 10MB.

I formatted it with exfat and a standard cluster size of 128KB because ext4 doesn’t work at my first try installing nextcloud. Maybe i have to try it again formatting it with ext4.

Or has anybody experience in formatting with exfat, maybe another clustersize?