Admittedly, this is an odd question but here's why I'm asking.
I use the Acapela Addon with several additional voices. When NVDA 2019.3 was released Acapela released an updated addon to accommodate the new version and this update worked perfectly and it continued to work with 2020.1.
A few days ago I visited the Acapela Web site and saw that there was an update to their addon. I downloaded and installed the new update only to find that NVDA reverted back to the Onecore voices and the Acapela addon no longer showed up in the list of synthesizers. Puzzled, I looked at the Manage Addons option in the Tools menu. I saw the addons but the status indicated that they would be ready upon a restart. Restarting NVDA and even the computer itself did not fix this problem.
I tried removing the Acapela addon along with all of the voices which were installed and even installed the older 2019.3 compatible version but this did not fix the problem.
Reinstalling NVDA from the 2020.1 installer also did not correct this problem.
I then decided to see which addons I had installed and began removing them but with no success.
Finally, I had two addons left: Clipspeak and Clip Contents Designer.
I wish that I had removed one addon at a time so that I could determine which addon was causing the problem. Instead, just wanting to get my Acapela voices installed I removed both of them and then reinstalled Acapela. This time the voices installed and worked perfectly.
I remembered that the CCD addon often wanted confirmation before copying something to the clipboard, something which I honestly found annoying but this is what made me think that an addon might be getting in the way of Acapela trying to install as I wonder if it was doing something with my clipboard but was being blocked by this addon. Of course, it may just have been something else with the addon itself and not being directly related to the clipboard. I should also see if these addons have been updated since the versions I was using. I just wanted to know if others have encountered similar issues where the presence of an addon might impair or cause problems with the installation of another addon.
Blindness Assistive Technology Specialist
JAWS Certified, 2019