Ukgc need to clamp down on this they go on about fairness yeah right this is the ultimate fuck you to players. Its vile they can just remove it no word just gone I am shocked to see bonanza is on there at the normal rtp still.
There's certainly an argument to be had, in that any slot with an element of persistence will never achieve its advertised expected RTP% if it has ever had a client-side update that has wiped the player's progress.
Therefore you could make a case that the slot in question was non-compliant because it could not and did not return its stated RTP%. I would use this angle in your complaint.
This topic was touched on years ago when it was discovered that some slots where you have to collect stuff could only return the full advertised RTP% if millions of spins were played on it, which is unfeasible to the average player. I don't think anything got done about it other than discussing whether an RTP% range should be shown instead which would cover how far the player had built stuff up, but I don't think it was as simple as that.
This is a different kettle of fish entirely though - player are having money taken off them through no fault of their own and without any means of recourse. That slot would be live on well over 100 online casinos and any update that wipes progress would affect thousands of players, even if it's for mere pennies in some cases. It's a modern day version of a fruit machine being taken off the floor for something else after someone had lost money in it.
There needs to be a rule for these games whereby to achieve certification at a Test House there should be a mechanism built-in so the true average value of any erased progress can be automatically calculated and added to the player's account if such an instance occurs. If they can't implement that functionality then they shouldn't be able to deploy it for real money play.
If people were collecting supermarket stamps to be able to buy a new TV, and the offer suddenly got withdrawn overnight without warning and your stamps were now worthless, there would be a national outcry and probably some sort of ombudsman to complain to.
I would urge players to moan like fuck about this to whoever they can, because it's clearly not acceptable and needs to be addressed properly by people who know what they're talking about. The BGC (Betting and Gaming Council) would be a good place to start.