After migration firewall occasionally blocks administrator's ip

Hi Friends,
I’ve migrated from one Linux Debian VPS to another one NC 14.0.x
Even before I perform each upgrade, after authenticating as administrator and clicking on any system entries, occasionally my ip was banned by the firewall (what’s never happened before).

On the new VPS I upgraded to NC version 17.0.7 but the problem persists.
Where I’m wrong?