It's a bug, submodules currently resolve their submodule's path against the main module's path instead of using their own path. I'll fix it in next release.
Im having similar issues in Monterey on OSX with a system that was working fine. I upgraded to monterey and all was good for a few days, then suddenly submodules not found. The message was saying that the submodules were expected in a folder that did not exist, eg ERROR) Submodule not found: /Volumes/Colins Samples/Flow+ 1.1.0/js/js/explorer/artificialharmonics.com_flow+_explorer.js
The aforementioned fix must have broken flow's implementation that was probably circumventing the bug. @gidash should be able to fix it (sorry for the trouble Marco).
How far do I need to go back? 1.15.7 still has part of the issue, ie the MAIN file is not found also for some reason it doesn't like port 5000 (in use apparently) and the point fails when I try to run anything.
I have been updating each time i see a new OSC version - ie its been working fine in previous 1.16 versions until now
(ERROR) Submodule not found: /Volumes/Colins Samples/Flow+ 1.1.0/js/artificialharmonics.com_flow+.js
v1.16.2 should be fine since the fix was introduced in v1.16.3. Flow is a very complex OSC-based app, updating OSC without making sure the new version is compatible sounds a bit risky.