Do the MMP files now open in Xmind or MindManager when you click on them? It's possible that Xmind has made itself the default program for MMP files. Assuming you are using Windows 10, go to Settings, select Apps and on the Apps menu click on Default apps - there are several options for changing file associations with programs.
In addition to the suggestion of Alex.
Mmp files were used before I believe vs 11 of MindManager.
The current file format is mmap.
So if you imported a xmind file and save it. It should be in mmap format.
Check if you have those stored in your default folder.
Thanks for trying to help. I have no solution yet, though consulted mm-help. I attach 3 screenshots to illustrate the probelm. As you can see the suffix is correct, but the icon showing is unfortunately labeld from xmind. Very upsetting when working with documents.
I even tried copy paste of the file to paste in in a new mm-file. It didn't work.