Now I get it... it's maybe other users who transfered their tumbled coins with a CPFP transaction with significantly higher fees and which bumped the effective fee rate of the tumbler's payout transaction from initially way too low 15sat/vB to ~44sat/vB. The tumbler pays the finally mixed coins to various users which used the tumbler.

Still pretty lame from FLYP to initially use an under current fee market conditions way too low transaction fee rate of 15sat/vB.

I don't know FLYP and won't use it if they have such a bad fee estimation. It shouldn't be the responsibility of their customers to bring the payout transaction to a fee rate that has a chance to confirm within a reasonable timeframe.