Update Unity causes new errors in WebGL (GL_INVALID_VALUE)

Good morning,

After updating from 2019.3.9 to 2020.1.15 (same for 2020.1.12) my WebGL builds comes with these warnings:



There is no further trace nor problems when running in the editor, and frankly I have no idea of where to start debugging this.

My goals are:
a) To understand the warnings
b) Get rid of the underlying problem(s)

All help is appreciated, thanks