Sorry to hear that you are experiencing this with your WIFI bands. We can understand the frustration caused and want to best help. I have had a look back end and I can not see any verification that your bands have been merged.
If you take a look at my message at 22/10/2020 09:34 (message 46 in the thread) - nearly a year ago - that pretty much sums up the situation.
In short, software version 9.1.1912.304 does NOT appear to have the issue - you may have luck triggering an update by turning it off and leaving it overnight before turning it on again. If you can't get it to update then a pin-hole reset will indeed be the only way of getting back in.
I can attest from personal experience that Virgin have no reservations about tinkering with customer's router settings but will then swear blind that they haven't. If you have noticed something is different, then the chances are something has indeed been changed.
In fairness to other posters, the App is known to cause a lot of issue however this is NOT one of them. This is a definite router issue.
Best of luck, I am well aware of how frustrating this issue is *AND* how frustrating their refusal to acknowledge the issue is.