I would not stop the HRT. It's a bit ridiculously over-cautious to refer you for a scan on the basis of that one incidence. I personally would have re-synced the progesterone and watched to see if weird bleeding patterns happen again. Only if they kept happening, would a scan be indicated really.
One thing to say is that you might want to increase your utrogestan if you have adenomyosis. It will help reduce the build up and should mean less painful cramps and periods. I know you think you fixed that with the herbs but if it happens again, I mean. I am on 300mg utrogestan continuously (except for 3-5 days to bleed) due to a history of endometriosis and this keeps me symptom-free.
This is especially the case if your estrogen has been increased, as your Lenzetto was. It's probable that this bleeding wouldn't have happened if your utrogestan was increased when your estrogen was.
Why do you think you are ovulating now? Is it due to egg white mucous? Our bodies on estrogen can do weird things. Usually we would not have high estrogen during a period. But on HRT, we can indeed have both our period (well, a bleed) and also high estrogen. The high estrogen causes egg white cervical mucous which we are used to getting when we ovulate. But it doesn't necessarily mean we are, now.
Even light spotting I would count as Day 1, since our bleeds can get quite light. Stop the utrogestan when that happens. Since you are now further along in peri, why don't you use utrogestan continuously except for when you start to bleed? This takes all the guesswork out of where you are. When you bleed, stop taking it for 5 days to allow the bleed to happen. Then start again. It will keep the lining thin better than sequentially and you don't have to worry about where you are in the cycle, plus it will help with the adenomyosis. It's what I do, in peri, and it works great.
I think this 'third way' of taking utrogestan should be more widely known. It is the 'old' continuous regime when you'd just stop for 3 days once a month.