It seems that only built-in low-code app icons are correctly being displayed in Cube and custom ones are being replaced by the default hexagon icon.
The below picture is self-explanatory:
Matthias Declerck [SLC] [DevOps Advocate] Answered question
Hi Conan,
By design, Cube currently resolves low-code app icons against the FabricMDL2Icons set (over 2000 glyphs).
If an icon name is outside that mapped set, then Cube falls back to the default hexagon.
What likely happened is a parity gap:
Web icon handling was expanded/ or changed (supports newer or broader icon definitions) without updating the Cube, while Cube icon resolution remained tied to the original FabricMDL2 mapping.
Matthias Declerck [SLC] [DevOps Advocate] Edited answer