Having just upgraded from a Fenix 3 to a Fenix 5x, it was disappointing to discover all sorts of problems with the F5's "race an activity" feature, at least for running-related activities. However, I've stumbled on a simple workaround that doesn't seem to be documented anywhere.
Here are the problems I've found. This is with software version 20.0.
- "Time ahead/behind" displays nonsensical values. As soon as one starts recording it jumps to some arbitrary value (always about 51 minutes in my case), and it hovers around that value for the duration of the activity.
- All course navigation features are disabled. This includes a course map and an elevation plot.
- "Race an activity" is only available before one starts recording a new activity. It can be stopped part-way through a recording, but it can't be re-started.
- Auto-scroll is always enabled, even if it's been deselected in the activity settings.
All these problems can be avoided with the following workaround:
- Enable the "Virtual Partner" data screen in the activity settings. The F5 will ask you to set a target pace, but this will be ignored when racing an activity.
- Select an activity type and hold the menu button, but don't select "Training"/"Race an activity". Instead, select "Navigation"/"Activities" (to race an activity saved in history) or "Navigation"/"Courses" (to race a downloaded course). Then select "Go" or "Do Course". You can do this before or after you start recording.
You can then scroll to the virtual partner screen and it'll work the way it's supposed to.
If you're running a course with lots of ups and downs it's better to race an activity saved in history. That way, "time ahead/behind" is based on how long it took to reach your current location last time you ran that course. If you race a downloaded course, "time ahead/behind" is based on your previous average pace for the entire course. This isn't very useful if the pace varies a lot during the course.