It seems i have a solution for all others with this problem:
** I am testing with different (in private) browsers do double check if the problem is solved. **
-Enable plugin (so all productproperty’s are visible and all = ok
-Export 1 product with the default woocommerce product exporter
-Disable the plugin. (content is gone)
-Import the 1 product back again. Yes, overwrite.
Now all my productpropertys are back again for all products. (so not the only one i exported and re-imported.