That does stump me. I asked about PRO because I was encountering an issue with individual points due to a new feature present this season for PRO uses, and that has to do with changing lineup order mid-series, useful in special circumstances in match point leagues. Again, I can't say this is definitely what's causing your issue, but it may be worth looking at.
You can check this on the score entry screen. The "Options" button at the top allows you to display/hide various things, and a new item for PRO users is the very last one, labeled "Position for each game". Check that box, then click "Update Form" and you'll see, to the right of where game scores would go, the numbers 1 through whatever, with a light green background. If you were to see anything with a different color, or grayed-out, you could then manually correct them. It may not even be the case for your league, but I'm brainstorming.
On my separate issue (posted recently) the fix was to do the above steps, then go through every team on that screen, which should at least fix the lineup order and thus (possibly) include that bowler's average.
Beyond that, the only thing I've ever suggested was to make sure that all bowlers have a gender assigned, and that the league was properly restarted for the new season. I have a hunch that you already have those things squared away, so I haven't mentioned this until now. But on that note, I've read in other support threads here that it had become necessary to re-create a league from scratch to correct some issues cropping up with leagues restarted over the course of several seasons, something I haven't yet done but I may bite the bullet and do that for 2018.
Now that the weekend is over, a CDE staffer may see this thread and offer their own suggestions. I searched the FAQ/KB and the closest I could find is the team average changing mid-series, which may be due to a league rule coupled with bowler(s) who bowled less than a full series during one of the first few weeks of a season. I doubt that's your case at all.
Always check, download, and install the most recent update of your software to ensure that issues may have been corrected.