Parallel Matomo and Piwik Pro tags

During the process of migrating from Piwik Pro to Matomo, I installed asyncronous Matomo tracking code onto a web page that already has Piwik Pro tracking. The idea was to collect a period of overlapping data to ensure that the transition goes smooth. I had tested the application before on more simple test setups, and it seemed to be working flawlessly. However with the production page, things went sour. Piwik does not work any more as expected, but collects data only a fraction of what is to be expected. Mind you, it has not stopped totally, there is still some data coming through, but much less than there should be. Matomo, on the other hand, collects plenty of data, yet I have no means to ensure that all the data is there. Data collected by Piwik seems to be a subset of Matomo data, so possibly Matomo works ok.

The question is, has anyone seen this inference of the two analytics software happen, and is there a way to tweak the Piwik to work with Matomo present? I would love to see data collected with both software over the Xmas period.