I had the same problem with the old version, I settled with my previous suggestion.
I advise you to save your vms and reinstalle a new installation, with the new version and restore them.
I have created several clusters on dozens of physical machines and it works very well.
I can even give you...
Why not migrate directly to version 6?
With the new version of corosync (no more problem on multicast or unicast ).
Look corosync3 and Kronosnet.
I have pointed that this is only done with a connection from the outside ( wan with Let'sencrypte certifcat).
The setting of my browser does not change. It's always the same whether it's for a connection internally or from wan.