I started checking into this and am finding instances where a history copy and paste from the darkroom filmstrip won’t paste the drawn masks. I’ve also had instances where DT crashes during that operation. Copy and pasting the history from the lighttable works fine - module settings, parametric masks and drawn masks are all copied into the destination file without issue.
I’m running 3.5.0+2475~gf6a211e96 on Windows 10, with an -O3 release build that was built as a “generic” package (ie, not optimized for my machine)