I am afraid you need to give us some more details. Especially what type of activity is it? With GPS or without? Best would be posting the link to the activity (after making it public).
OK, I checked the JSON data - there are no serious problems with the GPS coordinates, also the cadence is relatively regular and does not correspond to the abrupt pace changes. So far I did not find the culprit, but generally the watch resorts to calibrated indoor pace between any GPS track points whenever the GPS chip does not report sufficient accuracy. So I guess that's what happening here, but I do not know why the calibrated pace causing the spikes, is so high. One possibility could be that it got calibrated by error during a ride on a bike, scooter, or similar.
If you see it repeating on other activities, I'd suggest contacting the Support.
