Konqueror not interacting correctly with activities

Hello to everyone,
I'm the current Konqueror maintainer and I'm trying to make Konqueror work 
correctly with activities, as it did in the past.

The problem seems to have appeared when Konqueror moved from the "one process 
per window" model to the "single process with multiple windows" model. After 
this switch, a user reported that Konqueror doesn't interact correctly with 
activities; in particular, when stopping an activity, windows existing only in 
that activity aren't deleted, but just hidden.

I tried to implement a system which stores information about which activity 
windows are on, then using the signals provided by KActivities::Consumer to 
delete and restore them as needed (see [1]). This seemed to work correctly, 
except in a few corner cases where empty windows keep appearing.

To find out what was happening in these special cases, I looked at the source 
code for activities in KWin and in the activity manager and I noticed that, if 
I understood the code correctly, there's no reason activities shouldn't work 
with a single process, multiple windows application. Can you confirm whether 
this is correct? If so, could you please give me some advice on how best to go 
on investigating what Konqueror is doing wrong in this regard?

Please, CC me in any answer, as I'm not subscribed to this list.

Thanks in advance

Stefano

[1] https://invent.kde.org/network/konqueror/-/merge_requests/199