Yeah, this one's pretty common with multi-user setups, especially as user count grows — and it's frustrating because it's intermittent, not a clean failure.

"Server Busy" usually isn't QuickBooks itself freezing — it's QuickBooks waiting on a resource (the host's disk, network bandwidth, or the .ND/.TLG file locks) that's momentarily tied up by another user's action. With 6 users, you're right at the point where these random collisions start becoming noticeable even without any config changes on your end — sometimes it's not "something changed," it's just usage patterns shifting slightly.

Things worth checking, roughly in order of likelihood:

Host computer resource load — is the host doing double duty (running QuickBooks as a workstation too, backups, antivirus scans, other software)? Any background task eating CPU/disk on host will cause exactly this randomness.
Network stability, not just speed — Wi-Fi on any of the 6 machines (even one) can cause this. Wired connections for anyone accessing the file are far more reliable than Wi-Fi.
Antivirus/backup software scanning the company file folder — if antivirus or a backup tool is scanning the .QBW file while someone's trying to access it, this exact symptom shows up. Exclude the QuickBooks folder from AV real-time scanning and backup jobs.
File size/fragmentation — if your company file has grown a lot recently, condensing or a Verify/Rebuild (via QuickBooks Tool Hub's Company File Issues tab) can help.
QuickBooks Database Server Manager — confirm it's running the latest scan on the host; a stale scan can cause exactly this kind of inconsistent locking behavior.

If it keeps happening after checking those, tracking which user and what action (opening vs. saving) triggers it each time will help pin down whether it's one specific machine or a host-side bottleneck.

https://asquarecloudhosting.com/quickbooks-server-busy-error/