Problem with nfs shares

I've several nfs shares configured on OMV using the options "rw,subtree_check,insecure". The client machine runs Ubuntu 20.04 server with autofs to connect to the shares on demand. This works but if the OMV server is powered off and back on I cannot reconnect to the shares from the client without rebooting the client. I can ping the OMV server OK but no access to the shares. This is the same if I configure the client to use nfs 3 or 4.

Edit: I have setup a second device with the same packages as a clinet: nfs-common and autofs. Used the same autofs config files. All works fine on the second device. So OMV is not the problem (never thought it was anyway).

Any clues on how to fix this?

After several hours and much searching and testing I found the problem was UFW on my Ubuntu device. It looks thereore that on boot the nfs shares connect before the firewall is up, which was why I didn't think of this at first. Allowing nfs through the firewall and all good now.