I have an outbound channel with an BTC to Lightning exchange worth 2.000.000 satoshi, with enough capacity. I try to swap my 2.000.000 satoshi for the same amount, but on-chain. Lightningd splits the payment into too many subpayments, and eventually fails, even though the destination is only one hop away, and has enough capacity.
Tried a different, smaller one (0.01 BTC) with https://boltz.exchange/, and MPP pay seemed to work. The
pay command took 15-20 minutes to execute, and i was almost going to Ctrl+C it. I can send you guys the full lightningd logs (the first failure, then the second successfull one) if it helps you improve the algorithm. I guess you could merge #3936, since it's not the first time i tried paying 0.01 to that specific node, but it's the first time it worked.