2.6.4 - Yes, it is the propriety Lite version that comes with Ubuntu Store. I have since used Python to install another wallet* 2.9.3 which seems to be the latest available for Linux on the Electrum website
HCP:
I suspect that you had the the "co-signer pool" plugin loaded and running... this plugin sends the transaction to a central Electrum server waiting for the co-signer to open their wallet and automagically sends them the transaction to sign.
.. when you setup the Linux wallet, was that setup as 2FA as well?
-Just as a "normal" MultiSig wallet on the Linux. No 2FA,
In fact the Mac wallet required Google Authn, at some point, but I recall never having been asked to use it - I thought it was just to log in with nothing more. It's definitely something I started with, since it is there in Google Authn on my phone. I don't recall using it again, perhaps it wasn't set up right, so maybe we should ignore that.
*In attempts to find a remedy, I tried to create a wallet from my word seed in on my Linux PC. Nothing shows (just a zero balance) - no inputs.
Going back to the 2.5.4 wallet (the original one), I cannot see any further info to help matters. Am I in the wrong pool? I am connecting with the automatic connection.