I understand your frustration, still, I will implore you not to jump to any conclusion yet as the fault may be on their part or on your part. Gadgets/programs and internet services could be funny at times, and this might be from you or them, it will take a lot of repetition for you to make your conclusions.
No one is at fault here, there was no bug, and the systems worked as they should have. OP probably doesn't understand how live betting works because if he did he wouldn't find it unusual that it takes several seconds for the sportsbook to verify the results before accepting or refusing to accept a bet. Even closed markets are normal and it happens regularly in all sports. Especially if we are close to the end of the match or a significant point that can determine the final result.
Exactly stake is not at fault here and from the title of the thread, ops gave the wrong title to the whole thing it could have been better if oos have taken the time to read through the T&C of stake to be able to understand better where it states that the casino may or may not honour a cash out.
-So cashout payments are at the discretion of the casino and if you want to be on the saver side you should have your cash out earlier before the last 120 seconds to the end of the season if not the cashout will be removed or changed as the match progress the amount either decrease or removed.