Hi
I also had a horrible tracking experience today.
I used my Garmin 245 with version 2.70 with GPS+GLONASS and with update every second (I have disabled smart record).
I have installed Rails watchface (https://apps.garmin.com/fr-FR/apps/2700c6bd-f8fc-49b1-9654-97d9a750b094) and for this run I used the Dozen Run data field (https://apps.garmin.com/fr-FR/apps/9ff75afa-d594-4311-89f7-f92ca02118ad) and Single Field (https://apps.garmin.com/fr-FR/apps/640d46dd-12db-44d2-acfa-cb7eb9e840b7) alternating in between from time to time to see what's different.
I ran on the track close to the water. Please notice the track that my GPS watch recorded (color red) vs the real track I took (color blue). It's mind blowing how inaccurate this is!
If any of the Garmin people need any logs from my watch please let me know. I am willing to help you fix this issue.