I have tipjars that combine a non pbr material link and a pbr material link. Sometimes some of them will randomly show the pbr part as a blank material (no texture, no material parameters).

In the included captures you can see the 3 hearts on the left are fully blank, and on the right the 1 on the top is rendered normally while the 2 others see their pbr part being blank. (the rainbow part is non pbr).

This happens more or less depending on the days .. and one viewer can see them alright while an other viewer will see some of them rendered with a blank material.

This issue has been present for months, so it's not just the latest updates. Also it happens on PC or Mac.