Training effect suddenly showing up in one activity

I recorded two walk activities the other day with my Instinct Solar and, to my surprise, in of them Garmin Connect showed Training Effect!

I don’t understand how this is possible, since my Instinct Solar does not support Training Effect and this only happened in one of the two activities I recorded on the same day (both were 3.5-4km long and 1h5min long). 
This has never happened before (I’ve had the watch for almost two years now).

Watch is on 19.01 software. 

Here are screenshots from Connect
https://imgur.com/a/5VGeWaC/

Halfway through this activity that gave the training load, I tried to use the navigation app, pointing towards the start point of another activity that I previously recorded. The watch crashed (maybe because the memory was almost full?), then rebooted without losing what had been previously recorded. Maybe this event triggered some blocked feature in the watch software?  I don’t know.

Any thoughts?