For what it is worth, I too seem to be getting the same effect on my Win10 (1809, 64 bit) system.
It is not at all clear what event creates the files as (from the time stamps) they seem to appear in batches - I have 25 with the same time stamp, each 1579 kb - and the batches seem to appear once or twice a day, not regularly throughout the day as (for example) vps streaming updates are picked up.
I don't know whether they are from Avast or not, but I didn't see them before updating to 19.1.2360. The names are of the form prbE6D6.tmp with the 4 capitals/numbers changing.
The positive is that ccleaner (mostly) removes them.