V6.1 cannot be loaded by Remote Desktop Manager into a tab

I have been using WinSCP with Remote Desktop Manager (RDM) (Devolutions) for years. WinSCP is loaded by RDM in a tab with all my other remote sessions.

I have just installed 6.1 and RDM is unable to load it as a tab. WinSCP opens as a normal window and stays like that while RDM eventually times out and fails to load it.

I will report it to RDM but is there anything I need to tell them – as to what has changed between V5 and V6?

I have meanwhile reverted back to 5.21.7

I'm sorry, but I have no idea what change might have caused this.
All changes are listed in version history:
https://winscp.net/eng/docs/history
If they need any assistance with identifying the problem, let me know.
If you want, I can provide you access to nightly builds, so that you can try to find out when exactly the problem was introduced.