I am running Eclipse IDE for Java Developers 4.23, and then I have installed Erlang language tools IDE 0.60.4.v20210610-1117.
Maybe these software versions don't play well together. If I create an unused non-exported function for example, it will appear on the Problems listing, but the Location column has "line 0". Also there is no yellow mark in the left margin of the editor window. The same goes for compiler errors: no red marks.