Fluctuating voltage on Var 1

Could be fet issue.  Try a TIU Factory Reset first.  G

G. Thanks for weighing in.  Forgot to mention that I did the TIU reset already.  

Is the FET issue something a diy'er could do with an available part?  And even if so, how strongly do you recommend against that? 😂

As long as you have good soldering skills it can be done.  Just want to be careful of damaging traces.  It is a little odd your symptoms.  Usually one is shorted, but sounds like it maybe and open.   I would make sure no melted terminal plastic, good secure contact between post and the terminal ring.   Each Var CHannel has 4 fets so you need to determine which is bad or remove and replace all.  G

I've recently run across several FETs that are just not switching correctly, but they're not totally open or shorted.  They "sort of" work, but when replaced, all is well.

This thread might be useful.  If the FETs are "sort of" working might be best to replace all 4 at once as might be hard to diagnose...seeing as they can be had for a dime a piece!  Obviously need to transfer the heatsink hardware to the new FETs.  But as GGG says, some soldering/rework skill is needed so as not to damage the board.