This isn't something a problem that do talks alone with roobet but most gambling sites that does have dynamic fees will really be having this kind of common problem.
Even myself do have a problem on making some withdrawals when bitcoin network is hell clogged up. You would see $4 or eve $10 for a single withdrawal which
does really hurt specially if you are only making small withdrawals.For some this might not an issue but for majority this is indeed common.
The solution? Just wait up for the network to stabilize but well gamblers aren't really that patient though.
The biggest problem is the periods when you see it is not that bad, you withdraw, and the mempool gets clogged afterwards. Like for example this fall, right during this fall there were some people I am sure who wanted to move their money around, but it wasn't like this just yet, it was still doing decent, they moved their money around and suddenly the price of bitcoin started to fall which clogged the mempool and people who acted before, couldn't get in because same block had this fall calculated in as well which made it late.
So during a period when you should spend 10 bucks, you sent 4 bucks because when you did it, it was 4 bucks to send but afterwards it changed. I know this doesn't happen everyday, but there are some days this happens and it gets clogged because there are thousands of people who underpaid and it takes time for them to pass on.