Don't know if this is going to fix your issue, you can use option "float" to allow incoming packets from any IPs. From the openvpn man page:
Allow remote peer to change its IP address and/or port number,
such as due to DHCP (this is the default if --remote is not
used). --float when specified with --remote allows an OpenVPN
session to initially connect to a peer at a known address, how-
ever if packets arrive from a new address and pass all authenti-
cation tests, the new address will take control of the session.
This is useful when you are connecting to a peer which holds a
dynamic address such as a dial-in user or DHCP client.
Essentially, --float tells OpenVPN to accept authenticated pack-
ets from any address, not only the address which was specified
in the --remote option.