That is an issue in the validation, you could try replacing the validation rule with the microflow export from this link
You can put this in the folder Template / Column / Validation / document: 'ValidateColumnMF'
I wasn't able to test this myself, but this should work and allow integer/long to be compatible again. The code supports this, but the validation is no longer accurate.
If this works, this will be part of the next excel importer appstore release.
Thanks for providing a fix Jasper.
However, there is an error in the ValidateColumnMF you've provided but I was able to fix it myself. I created a bit of a dirty fix because I believe what you've provided should have worked.
The first validation in exl split 'mf type = member type' fails in my case because Output and Member are of the same TypeEnum but somehow they are two different instances. So
$ValueType_Output != $ValueType_Member.
I have changed it to
$ValueType_Output/TypeEnum = $ValueType_Member/TypeEnum and have provided a revised package.