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I go the following warning message in my openVPN server logs

WARNING: --topology net30 support for server configs with IPv4 pools will be removed in a future release. Please migrate to --topology subnet as soon as possible.

You are still using topology net30 in your server config file.
It is only used for real old windows clients.
Where each client has his own network (each with 4 ip's)

a better option, and in the future only supported is
topology subnet

Change it in you config file (usually /etc/openvpn/server.conf )