Hi Pavel, nice to meet you.
Thank you for reporting the issues you are encountering with mutable. I will assign this task to a colleague that has worked on adding support for the Grooms in Mutable and has also fixed some bugs related to the interaction that exists between Mutable and the level Sequencer.
In regard to the mutable Populations plugin, while we have plans on fixing it and, maybe, expanding upon it, we can not allocate time for it at this moment. I sadly can not give you an estimate date for it to be fixed, as I really do not know when we will have resources to allocate to that.
Again, thank you for reporting the issues you are facing with mutable.
Have a nice day!
Daniel Moreno