Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: rB0330d1af29c0
Short description of error
Grease pencil opacity modifier's opacity factor is not working (see video)
Exact steps for others to reproduce the error
Add grease pencil object
Add a opacity modifier
Try lower opacity factor
I tried with modes: stroke and fill, stroke, fill, uniform opacity, infulence layers / materials but no.