Unrecognised installed library - DataSpell -

Hello,

I am trying to replicate a repository which has several third party libraries. There is a problem with only one of them. DataSpell does not recognise the ete3 library even though it is installed. It displays 

Unresolved reference ‘ete3’

If you hover over the name of the library, a window pops up suggesting installation. I tried that too,  but nothing changes.

I am sure that the library is installed, because if i run python from the terminal and import the library, there is no problem with the import. Though it displays this message:

/home/path/to/python3.9/site-packages/ete3-3.1.2-py3.7.egg/ete3/evol/parser/codemlparser.py:221: SyntaxWarning: "is" with a literal. Did you mean "=="?

Any idea about this strange behaviour?