@rogge doubt it would be due to magnetic interference, think the issue is more around fused tracking which takes a fix every 10s, which is fine when you are walking, potentially hiking depending on terrain (not sure how well it works if vertical climb is steep). However if you using a bike, I am not sure it works to well, as you can travel quite a distance in 10s so if you are varying speeds etc, i can see it giving issues.
Try setting it to best (1s) and see how that does.
Also note that what you are seeing isn’t necessarily unusual as GPS while fantastic accuracy is only up to 5m. Watch antenna’s are tiny and often not pointed in ideal directions, and fewer satellite fixes (ability to select and use multiple satellite systems can assist i.e I can use GPS+Gallileo or another system for example) - as coverage depends on hemisphere and region, and terrain features, cloud cover etc can all make that worse.
While your blip (riding through the house) isn’t great is isn’t really that bad either. Your general track is correct, and would focus much more on that rather than precision accuracy which you are unlikely to get without using a device with a much better antenna.