Explorer: preview thumbnails aren't working properly - Acrobat XI

[philipp30000]

Very annoying problem: Win10 Explorer: Preview-icons instead of generic PDF icon is only wrking here and there. As i have a lot of pdfs i realy need the preview for quick orientation. 

If important: I use large PDF files, output of copy/scanning-machine, 0,5 to 1gb. I let them all run trough Acrobat XI scan optimization tool and text recognition. Saved the first time i see the preview icon. After computer restart the next morning: generic icon. 

Please help! we have 2020!

[philipp30000]

Update 1: Sonrry, it's not Acrobat XI anymore, it is Acrobat 2017. Will Upgrade to Acobat 2020 help? As i need EDU-Version Acrobat DC is no Option. Thanks.