Hi Vitor,
Does server error log have any information about blocking of the connections?
Maybe it could give you a clue of what is happening.
MySQL Server can block connections if it gets unsuccessful connection requests from the same address. After certain number of errors the connections for this address are blocked (check sysvar_max_connect_errors):
https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_max_connect_errors
Normally the blocked hosts can be reset by host cache flushing:
https://dev.mysql.com/doc/refman/8.0/en/host-cache.html#host-cache-flushing
This does not explain why all hosts are blocked though.
Could be a bug in the server, which is pretty old. Or there could be other contributing factors.
I would recommend starting from inspecting the server error log.
Thanks.
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Best regards,
Bogdan Degtyariov