So far, every time that you get a voucher instead of the private keys to your chips has been because of lack of chips. I assume that for some reason there is very high demand right now, as it is not usually this way. The only time this wasn't the case was back when the fork to Bitcoin Cash happened, which forced ChipMixer (and many other services) to close and wait for security purposes. You can always email them about it to be sure and try to save your session in case it takes longer than it usually does to top up the chips.