I actually think this might be more on zeus' side, but I'm really not sure. Mutiny seems to receive the payment correctly.
Discussion
Does that appear after the payment completes?
I've reproduced it 3 times now. 2 of the times, zeus responded first. The middle time, mutiny responded first. All times were really slow.
lnd logs don't really show anything out of the ordinary. I don't getting this error paying to other sources.
Using "Bitcoin Atlantis" (120879c1233789679a4ed9b47ba557f8da3d4577b4e0b3f61fa5afd3137b824a)
Just sounds like a payment slowness. Not an LNURL problem, just lightning liquidity issues. We don't run the federations or lightning gateways, so nothing we can do here.