Hi, hmm .. I may suggest trying some BT GPS app from Google Play. Its developers should be more specialized in "BT stuff" so it may work better than Locus. Such apps are then able to share received locations to the Android system, so to Locus Map as well.
And GPS suggestion ... well, I've stopped to use BT GPS completely maybe 3 years ago. Precision of modern phones is amazing and my older Pixel2 has still precision the same as all basic BT GPS. And battery? Well, one small power bank solves most of the problems. I just think, that if you do not want to use some special ultra-precise GPS device, modern phones are more than usable. But ... no better suggestion sorry. I've used QStarz device, but not sure if they have any new devices available.