Honestly, my observation has been different in this forum from others posts, and also based on tracker data. Mostly single applications are getting invites a lot. I know few of my friends who applied in late 2020 got their test invites already (both single applicants.)Friend of mine told me that they're clearing the family applications first, because they can clear 3-4 in one time. Probably that's why all the single applicants applications are getting delayed. could be totally wrong
At this point, it totally seems random.