File is produced from keyboard (mic is through the keyboard for second vocal track) to Lexicon box to computer. The file is distorted, weak and lots of reverb when played on phones, laptops, kindle, etc. but plays fine on desktop computer. However it plays correctly on ANY device if the file stereo track is split and either channel is inverted. That’s the fix. The question is why after 8 years using Audacity an invert of a channel is required to correct this problem when no change in equipment or method of recording.
Somehow one of your channels is inverted so inverting again (or inverting the other channel) will put them “back in-phase”.
What kind of connection(s)? Any adapters?
Something is probably wrong with your left & right connections to the Lexicon.
Do you have a link to your keyboard and/or Lexicon manuals?
There are ways to foul-up mixing & matching stereo & balanced connections/unbalanced connections. Or sometimes just a mono-to-stereo connection.
i.e. A TRS connector is used for both… A TRS connector has 3 connections/wires. With a stereo connection they are left, right, and ground. With a balanced connection there are 2 differential (out-of-phase) signals, plus ground. With balanced stereo connections you have separate plugs for left & right.