Check your PHP Version.
I changed my PHP version to 7.1 from php 5.5 and it works well again.
If you use the file managers of some good control panels, you can avoid such scenarios in future. Or if you upload the whole zip, then unzip on server and move the files, it will be faster. Uploading each file of the tens of thousands can take hours (some reported).I found out, my issue was, that not all the files were uploaded. For some reason, my ftp client uploaded files to .../app/app instead of .../app folder.
So I was missing many files.
I reuploaded and I'm good now
I just located this Doc with a Google search.
Well there are a lot of documents out there for MW. Finding the right one is the biggest problem. Is there an Index somewhere for the MW support docs?
I can't find the option to display lists in alphabetical order (especially in the pull-down during campaign creation).
We have 260 lists so that would really help.