This kind of behavior is mostly exhibited by scam casinos since what they care about is to steal from their customers and if they find out their secrets had been exposed, they will have no option than to delete the users account and leave no trace for the users. Being careful is what we need to keep eyes on so that we are not going to be a victim of bad casinos that will deprived us of all our struggles after referring users to the casino and not getting compensated. If we don't he same in a reputable casinos, we might even get more bonuses from the team from being a top referrer.
If a casino often change the referral terms by directly reducing the pay percentage at close to the end of the month, then that likely a proven case of attempt scam casino, and you should avoid such sites from that very moment, since reputable casino will not change anything concerning the terms of service or payment percentage at frequent and suspicious manners just like the shity casinos does sometime.
It is very easy to spot the bad actors in the market unless you allow yourself to get carried away with their enticing offers that may never come and are just a means to rip you off your balance or get it stuck along the line and that is the reason why you need to avoid them in the first place.