Ok...so it has to do with multiple Microsoft Mashup Evaluation Container running in Win10; up to 7 instances when I have closed the Excel file(s). I closed these container files via Task Manager. Then re-open the file, the data model was restored; Powerpivot option was on the ribbon.
However, now I'm getting multiple Microsoft Mashup Evaluation Container files each time I open an Excel file..the container files hog all the RAM and freeze up the file so that I can't save and exit. I'm running Excel 2016 from a laptop, accessing my files remotely via VPN from a network drive.