Added network/hosts cannot connect unless removed and re entereds

Howdie all,
an IP address is added in Firewall / Networks as trusted…
Suddenly, they can’t connect so I ensure their IP has not changed.
It has not.
Only way to resolve:
Remove the IP (Select and delete selected entries)
re add it again.
now works.
Any ideas why / how this happens?

Checked fail2ban and the IP was not listed as blocked.

Thank you all

Anyone?
it continued to happen… remove an IP from the HOSTS and re added it to work…