Statistics timeout in OJS 3 (Generate Custom Report) on journals with a large number of back articles

I am working with two journals each with in excess of 10,000 articles in back issues. We have recently upgraded from OJS 2.4.8 to OJS 3.1.1-4 .

In OJS 2, I had to pull statistics (Timed Views Report) for these in tiny little chunks - 3 days at a time - then sum up the total downloads and abstract views. If I tried pulling a larger window of time, like 2 weeks or more, then I would get a timeout through the browser and not statistics.

When I go to pull these reports in OJS 3, I can put in a full year (I am trying for fiscal year). Then, OJS 3 gives me a very low number. For example, in fiscal year 2017-18, a journal which had 188,704 PDF downloads with statistics from OJS 2 Timed Views report (pulled in 3 days chunks and summed), now has 14,153 PDF downloads when I pull the statistics with OJS 3 Generate Custom Report (Article File Downloads, pulled for the entire fiscal year).

If I start chunking up the fiscal year in OJS 3, and pull one month at a time, then I get dramatically higher download numbers.

I think that what is happening is that OJS 3 is timing out, and then giving whatever it has so far when it times out, rather than giving an error message.

Is there a way for me to know whether the Generate Custom Report timed out or not?
I would rather have the error message and know that the report is incomplete, and I need to slice thinner to not timeout, than to have a report that looks complete but isn’t and I have to guess.