Not really anything to do with your problem but those are not Sanwa buttons just that you know.
Most won't really care but if you are into arcade sticks or arcade machines then you'll know the quality differences.
There are no Sanwa buttons that look like that and I guess they'll feel different when pushed. Look it up on google, search for OBSF-30 and you'll see what i mean.
I myself own 2 self build arcade sticks and I bought Seimitsu and Sanwa buttons and sticks and they cost way more then that set price.
For 33 GBP you could probably get 10 buttons. Looking at the sellers info...no surprise, China.
Like I said not that most mind but once you have used quality stuff you won't get satisfied with that and it kinda angers me that they actually write Sanwa Push button in the title description.