It says eg
Warning Filesystem: warning (Your server is using an NFS filesystem. This means Matomo will be extremely slow when using file based sessions.)
But we are not using file based sessions anymore anyway.
Could also simply remove the message but not sure what the point of having this check is then. Of course could say in general using NFS may be slow.
Reckon the diagnostic is still valuable, even when not using file sessions, because even just storing the tmp/ cache folder in NFS results in slow downs. Maybe we could change the second sentence to
This means Matomo will load slower than it should be.