Just a follow up.
A friend had a similar problem as I did i.e. the track visibility turning off & not sticking after closing Locus Map and then reopening.
I'm reasonably sure it's related to the problem described:
https://help.locusmap.eu/topic/30937-maps-vanished-and-error-12569-on-downloading#comment-124693
We applied the suggested "Most reliable solution" & their track visibility is now working properly.
A friend had a similar problem as I did i.e. the track visibility turning off & not sticking after closing Locus Map and then reopening.
I'm reasonably sure it's related to the problem described:
https://help.locusmap.eu/topic/30937-maps-vanished-and-error-12569-on-downloading#comment-124693
We applied the suggested "Most reliable solution" & their track visibility is now working properly.