So, after feeling like I've had the run around from the club today with mixed messages, I finally got to test my Season Ticket ticket this afternoon.
Several other people tried during the 10 minutes or so I was there, and not one persons phone worked using the NFC. I tried this both by having had the app already open, and also by closing/reopening. However all seemed to work fine with the barcode, although you had to find the right distance to put your phone into the slot.
There were also people there that were querying where to find transferred tickets, and also someone who had multiple tickets on their phone, and whilst the steward tried his best to help, he didn't really have the answers himself.
If you've got your own card, on your own phone, then I'd say just make sure you know where to access the barcode and all should be fine, if still slightly slower than the previous way with physical cards.
If you have a situation where a ticket was transferred to you and it's not on your card/phone, then definitely contact the club beforehand.
If you have multiple tickets on one device, eg: Adult/child, then I'd definitely make sure you can access each ticket/barcode individually on your phone.
There was also a fella who had a new photocard and his worked fine.
Finally, and perhaps ironically, I tried my old Season Ticket card, and that worked perfectly!