Which particular issue would that be, you haven't said.
You can't disable IPv6 on the SH2, the log entry is just the hub soliciting to find IPv6 devices on the network.
Have you given the camera a static IPv4 address outside of the DHCP range of the hub on the camera itself.
The new hub will have a different wifi passkey to the old hub.
Might be worth factory resetting the camera and setting it up from scratch.
Looks like I'll have to either ditch the camera or buy a new Hub 5 router.
It would be much better to spend your money on a different router which is much easier to use.. Prices start at about £40 for a single band wireless unit, and about £70 for a dual band one.
Unless you really must have 5G wireless, the single band one is a better option.
@pjkpjkenne There are a couple of other things you could try before getting a different router.
Although limited to 3 channels on the SH2, you could try changing channels manually to see if that helps, you could also try Mode 2 and Mode 3 in the advanced wireless settings.