Thanks for the reply.
I actually figured out a workaround … I created another 1:1 NAT rule with OpenVPN as the interface. Otherwise the rule is the same for the 1:1 NAT rule that sends public traffic to the private IP.
NB: for OpenVPN clients who do not use the "send all traffic over the VPN" option, accessing the public IP is no problem, but for clients who DO send all their traffic over the VPN, this is necessary to connect to public IPs. In a few critical scripts which we share with our customers the public hostname/IP is configured, so staff who might use those scripts from a hotel/airport/conference while tunneling all traffic to the firewall make this configuration requisite.