Actually, I am surprised that stake offers something like deposit bonuses now, I never heard of that. Thought this might be a scam but since you say the bonus money was added to your account I guess it's not.
This is not new I have known this for a long time yeah about 2 years, so this is a collaboration between Stake and third parties/affiliate that's why 'Welcome Offer' is available in our account or other special code. So to see this ads you can find it on etherscan.io or other sites like this screenshot
https://talkimg.com/images/2024/08/30/9NkVI.jpeg and the requirements of each affiliate are different depending on which code you use between 35x or 40x
Regarding this problem, yeah this often happens to several accounts that claim bonuses due to suspicions about several things multi account, arbitrage or others I just wonder why support doesn't explain the actual problem. Usually if the betting amount is limited or lowered the indication is that the user is using arbitrage betting or betting on odds 1.01 dominates the betting slip on sports so generally if we claim a bonus the minimum odds are 1.4 and 1.5 here I am not saying OP did anything and I am just explaining based on my experience and some friends, so it would be better if OP posts some betting slips.