DietPi & nextcloud large file semi-crashes it

I don't exact cause of issue, which is why I need help. I feel like it's because of large files or something about overloading, but it doesn't seem to crash syncing small stuff, but when it's a gigabyte on my phone especially but also on my pc sometimes, it just kinda crashes, hard drive is still blinking, internet is also blinking, no response from ssh nor nextcloud server, it just times out, I have to unplug the system which is a risk and let it boot again to fix this issue. What could it be, please help, I don't think it could be a problem with the router, but idk

My guess is that it could be overloading the ram trying to transfer larger files. Which Rpi do you have and how much ram does it have? You could try sshing into it before doing the sync and watching ‘top’ to see what happens before it crashes.

Yup and look at syslog or dmesg