Voltage on modules

Did you happen to balance the HV battery by using a DIY grid charger/discharger, or equivalent?

There are only 27 modules listed in your post, unless mistaken.

 

A couple issues to think about. First, those voltages are pretty high, meaning the battery was recently under a "being charged" condition. That tends to cover up problems. Second, voltage readings by themselves are poor for determining a weak module. They're good for detecting a "failed" module, but not a weak one.

As an example, I run down to the local store and buy some D, C, AA and AAA batteries. I throw my multimeter on them and they all measure 1.5 volts. Yet an AAA battery is only about 10% of the capacity of a D cell.

This is what happens to an HV battery over years of use. 28 individual modules that tend to diverge in capacity over the course of time and usage, until you have some D, some C, some AA and some AAA modules. It's those low capacity modules that cause the problem.

 

Red triangle- have you discounted a failed inverter coolant electric pump? That's the typical issue causing the red triangle.

 

The master warning light (a/k/a red triangle) can be illuminated for a myriad number of problems. A failed invert coolant pump is but one. Reading the codes is the best way to determine why the light is on.

In this case the master warning light has been attributed to battery issues.