New sites having the default Twenty Fifteen instead of the chosen blog template

New sites having the default Twenty Fifteen instead of the chosen blog template

There's a problem with the New Blog Templates plugin on my website. I mentioned the issue before, and was hoping that it will fix with an update. Randomly, new created websites have the default Twenty Fifteen theme, instead of the one selected via Blog Templates.
Actually, that's the main reason I still have the Twenty Fifteen theme installed. Because before, those who encountered this issue would have gotten just a blank page, with no theme at all.
Can't find any pattern on how the Twenty Fifteen replaces the Blog templates' theme. But looking on the new created websites/accounts, I had the unpleasant surprise to see that like 1 in 4 websites (at least) don't get the New Blog Template.

Is there anyone who had this issue and managed to solve it?

Thank you