Set up a new server with Belt Upgrader https://mods.factorio.com/mod/BeltUpgrader

Robots will attempt to upgrade belts, but will place belts on the "underground" map that Belt Upgrader provides, then get stuck in a seemingly infinite loop trying to upgrade the above ground belts

Bug has also been reported to the other mod authors forum here https://forums.factorio.com/viewtopic.php?f=190&t=38757&p=384799#p384799

It sounds like BeltUpgrader is looking for "faster" belts and finding the fake belts that Beltlayer adds to enable construction robots to build belts with underground belts, instead of finding the actual belts.

I could add a fairly simple check so those belts don't get added to the list of candidates. What are the fake belts called?

As far as I can tell, they're named the same as "regular" belts (Transport/Fast/Express)

The "connector" items for the mod are named "Underground Belt Connector" and do show up with a (slightly) different icon in the crafting menu however

@Mylon: The internal names are beltlayer-bpproxy-*
So beltlayer-bpproxy-transport-belt, with localization "Transport belt (underground)" and so on.

@intelminer, I made a test version of Belt Upgrader. Can you try it please?

https://www.dropbox.com/s/adm3iskuym6sizq/BeltUpgrader_0.9.10.zip?dl=0

If this works, I'll publish it.