Quote from: ethereal1m on Today at 04:38:03 AM

4. Try to increase receiving capacity by doing submarine swab again. But on the electrum history tab it says forward swab 6.4 mbtc and channel detail said it can receive 0.179 mbct.

This will happen if you clicked the "lightning icon" in submarine swap window, that'll swap the BTC and Lightning icons switching it to forward swap.
Forward swap will decrease your inbound capacity instead.
Since it worked and decreased your inbound capacity, that confirmed that you can receive LN funds before the forward swap.

Quote from: ethereal1m on Today at 04:38:03 AM

2. How to fix "no path found error"?

Mostly it's a channel routing issue (the solution is the post above); but since you've done a max forward swap, it's your inbound capacity.

Quote from: ethereal1m

1. Why did I fail to receive 4 mbtc even though the channel said can receive 6 mbtc?

It could be a channel routing problem of the one who's paying you
or your channel(s)' status aren't open yet when you tried to receive, can also be a bad connection.

Based on personal experience, I've been experiencing those "no path found" error by random chance specially if the wallet has just opened.