I think it would have been noticed by lots of listeners on the day it was sounding poor (Friday 1/2/2019?) as it didn't sound good at all on that day.
I did search the internet for problem reports for R4 on 198kHz and it had already been reported as a problem on at least one site for that day. I can't remember if it said it was noisy or if it said it was distorted but I think it was this site here that reported the problem:
http://www.radioandtvhelp.co.uk/inte...radio/am_radio
So it does look like the problem gets noticed and the time of the report appeared to be just before it was fixed on that Friday afternoon. However, I can't actually find that report today so maybe they delete them after a while.
I recorded the pips again today and demodulated them directly in the analyser and the analyser can show the modulation envelope for each pip. Each pip looks to be about 100ms long and the final pip is about 500ms long. They seem to be spaced exactly 1 second apart on the leading edge of each pip. The pip envelope has a rise and fall time of a few ms.