Hello and Welcome to the Discussion!
It sounds like an interesting issue - I was unable to recreate it.
I created a central model, closed all of the created worksheets and as I saved it I went to the options (image attached) and set the Open worksets default: to last Viewed.
When I opened the model all of the worksheets were closed.
I opened them all and sync'd to the central, then closed and reopened - but the worksheets were open. How they are kept at close I am not sure.
Even after opening them with them closed - have you gone to the collaborate tab or the worksharing shortcut on the status bar and just open them? Instead of closing and opening and specifying what is open? Just a thought...
LD
If this helped solve your issue - remember to 'accept as solution' to help other find answers!
You can't think AutoCAD and run Revit.
Email: LisaDragoEE@gmail.com