Today we went for a really short walk and at first there was the ankle irritation; I was wearing my hiking boots which have quite a different wear pattern to my running shoes. Gradually it faded but it did remind me that things aren't right. During some roller work this evening I even thought I could feel the peroneus longus tendon issue in the other leg! I suspect I was imagining that a little.
A little more online reading suggests that forefoot and midfoot strike is more likely to irritate the muscle than heel strike, which makes sense, so perhaps there's a bit of that to blame? I've also spotted a few hints linking peroneus longus tension to first ray metatarsalgia (i.e. pain on the ball of foot) so my observation of that is nothing unusual. Importantly, if that is present it's more likely that the muscle is tight and making things worse. I need to find some good literature to support these aspects!