I didn't investigated this, but my first though is that these users have a poor channel reachability to coordinators nodes. Do you think it's another problem?

Sorry @KoalaSat, I was not clear. The issue is not payment failure. When the client waits for buyer invoice, it does not accept the invoice when it gets pasted from alby. So the channel capacity should not matter. @npub1s277...dsym do you remember if there was a particular error popping up?