I had an intuition that running both wallets on the same PC might have had something to do with it, but I dismissed that notion. I'll try running one wallet on the VM and see if that works. If not, I'll use a laptop. I'll report what I find.
I have the same issue I've been testing things on lightning to send the testnet coin but I'm still failed until I stop testing so many things to make the lightning sending works. I was planning to test it before with BTCpayserver but since the issue still occurs I gave up.
I'm following this tweet
https://twitter.com/lukechilds/status/1195739189075005440xAnd waiting for him to respond to how he made the lightning payment worked.
Try to contact him through twitter and maybe this time he might answer you.