I am currently trying to solve the CoinFlip challenge on the Mumbai (Polygon) network.
It seems however, that the block time is too fast on this chain, so by the t ime I submit my guess, the block has already changed most of the times. As far as I can see on the polygon explorer, the blocks last 2-3 seconds most of the time.
Did anyone solve this problem on the Mumbai network ?
My solution works on my local test network using hardhat, so I am pretty sure I have no errors in my code.
Hi, welcome to the community! 
IIRC, I think this puzzle tries to tell you that if you want to generate a random coin by something in block chain, it is not a real random result, in this puzzle, the block number can be easily accessible, so actually, you already know the result of each guess in advance.
And I think it does not matter on the polygon, if you think it is hard to do this manually, you can write a scripts to do this automatically, so then you can control the time to send transaction.