Writeback disk bad sectors
If clients are randomly restarting with bluescreen and stop restarting after deleting all writeback files or formatting the writeback disk.
Then, you need to check the disk health, it may have many bad sectors. When the writeback file of the client is written to the disk and encounters a bad sector, it won't be able to write it on that sector which will cause client lag as well as blue screen and restart.
To fix this, you need to replace the writeback with a new one, possibly an SSD if you are using HDD currently.