When I went to the physio he said it was probably down to a weakness in my calf.
Another thing he said was concentrate on keeping my feet loose when running. If it carries on, and when social distancing is relaxed, I'd really recommend going to one - it helped me loads.
I do weighted straight and bent leg calve raises - 2 seconds up and three down. I also hop on the leg to 180bpm metronome. Both are helping currently.
I had the same thing last year and this stopped it.