I use the latest stable firmware on Beryl (3.215) and the memory usage raises to about 89-90% when using the SMB to transfer files to a 512 GB sd card on the router, which is normal, but it doesn’t drop when file transfer (read or write) not in use and remains high causing it to reboot.
If you use SMB frequently, we recommend that you try upgrading to version 4.x. This version has improved file sharing features.