Unfortunately, this is something out of ChipMixer's control. Fees are terribly high now, 750 sat/byte is needed for a fast confirmation, and anything smaller is just ignored by the miners.
That means a small transaction with 1 input and 1 output requires almost 0.002BTC fee.
I expect fees to get lower again at some point, but I don't expect it to happen any time soon. Maybe next Sunday again? Either way, just keep extending your session every day until it's confirmed.