Google Fit suddenly not counting steps anymore

Hi i have been using the app since the beginning of 2019. Up until 2 days ago, it worked pretty well then suddenly it has become much less effective in counting steps. I have been taking part in a local walk challenge in which Google Fit syncs with Movespring. Every day I have done between 8000 steps and around 24000 (once 34000) so I got a good idea of how many I could do on a workday compared to a weekend day. Suddenly yesterday and today it has recorded under 5000 steps and no heart points at all. In comparison, a separate pedometer has recorded 8-10,000 steps each day. Any suggestions would be welcome because I am baffled. By the way my phone is a Samsung J6 not J7 but J6 wasn't listed when I registered.