Chromium StartsOnDesk behavior depends on browser content

I have a problem making Chromium start on the desired desktop. I have two separate sessions using two different class names that I want to start on two different desktops but sometimes it ignores the StartsOnDesk command. Interestingly it seems to depend on the content of the browser. This is what I get when debugging:

BugOpts ExplainWindowPlacement On

Starting chrome gives me the following:

[fvwm][__explain_placement]: placed new window 0xe00007 'New Tab - Chromium':
  initial size 1905x2140
  desk 0 (current desk)
  current page
  position 10 10  (used program specified position)

[fvwm][__explain_placement]: placed new window 0x18008f7 'Warning':
  initial size 450x96
  desk 0 (transient window placed on same desk as parent)
  current page
  position 1323 1052  (used program specified position)

After removing ~/.config/chromium:

[fvwm][__explain_placement]: placed new window 0xe00007 'New Tab - Chromium':
  initial size 1905x2140
  desk 1 (specified by style)
  current page
  position 10 10  (used program specified position)

[fvwm][__explain_placement]: placed new window 0x1800d00 'Warning':
  initial size 450x96
  desk 0 (transient window placed on same desk as parent)
  current page
  position 1323 1052  (used program specified position)

Does anyone have an idea why Chromium behaves like this? Are there any additional Style parameters that I could try to add? Any help appreciated!

Hi @hrnick

It’s probably a problem with how Chromium sets its class. Are you using FvwmEvent or the InitialMapCommand style?

Thanks for your reply @thomasadam!

I might have missed something, I’m using neither of the two, just Style:

Style Chromium-test               StartsOnDesk 2

Adding InitialMapCommand didn’t change anything regardless.

Some additional information:

$ cromium --version
Chromium 87.0.4280.66

$ fvwm --version
fvwm 2.6.9 [...]