NCP USB HDD switches to read-only

Hello everybody,

I am working on this for months but am not able to get Nextcloudpi working stable on my Raspberry 4. Here is my setup:

Nextcloudpi 1.31.0
Database: mysql
Raspbian Buster
2 Windows 10 clients (3.0.2)
2 Android clients

Everything seems to work just fine. Lets Encrypt certificate, external storage, user management, port forwarding, automatic uploads on the Android clients and downloads on the Windows 10 clients.
But whenever I try to upload something on the Windows 10 clients (regardless if 20x 2MB files or 1x 2GB file) there is a big chance (not always) something on the Raspberry switches to read-only for the USB HDD and that it was.
After a reboot Nextcloud is running again but no client (also Android) can upload something without crashing the system again. Only restoring a backup helps in this case.

I googled this problem again and again but there is no real solution to it. As my frustration rises I hope someone here is able to give me a hint.

Thanks a lot.

I’d check output of dmesg and syslog, look for i/o errors.
Could be your usb drive is failing or under powered. Does it have its own powersource?

Thank you.
“dmesg | grep -i usb” is not showing anything. As well as “dmesg | grep -E “memory|dma|usb|tty””
In /var/log/syslog there is also nothing related to USB or the mounting point of the HDD.