I think this was to be expected sooner or later. I used Muun for a while but it was known that their model would not last long under a high fee environment. I am using Phoenix now, but opening new channels to get more inbound capacity is expensive, so many transactions do not work. Not sure if this kind of wallets (I mean, LN non-custodial wallets) will fix it soon. Perhaps some kind of swaps with Liquid would help.