yes, I was downloading with a correct account and looks that it was also set as a prior when entering the playstore settings. also if I click on the transaction status, it shows the Pro is in purchased list.
in the link you shared, there was a link to workaround, but the page does not exist anymore.
anyway reading though more, as written, that developpers does not have really a control what account is used to validate the app if purchesed. And looks that in my case, when I install/reinstall with active account, license check descends to another one where the license is not presented.
As my workaround, I have disabled the additional google account, and now it starts looking better.
I added the one without license again, and Diarium keeps the Pro status for now.
At least, i know what is happening. and how to eventually workaround it. Good