20.26 no radar gauge with RTL 515

Unfortunately I experienced the same behavior yesterday with an RTL 516.

It was always changing between those two modes, very annoying. Please fix.

I am not sure if you have seen my reply in other post.

Could you check if pressing Lap button, makes any difference. 

I have observed the same as you report, but pressing Lap seems to fix it (at least for a while)

It might help Garmin to understand and fix that. 

I have the same problem with RTL 515, the bug reported in beta is still here. This bug must be taken very seriously because it is a safety feature for road cycling. That's why we decided to buy a radar lights.

I had the same issue when riding yesterday.  No radar indicator, just the small vehicle approaching text.  It definitely made for a much more scary ride due to the fact that I had to constantly be checking my mirrors or turning my head.  Please fix this.  

In this case a temporary solution could be use auto lap and set the  lap distance based on the average of your speed

I have autolap turned on already.  Those notifications worked as per usual, but radar indicator functionality was still not working.  

I can confirm that using Auto Lap allows you to keep the gauge always on as long as you set the auto lap to a suitable distance. Today during my usual ride I was able to measure exactly the time that the gauge remains active, in the case of my forerunner it is exactly 2 minutes. That said, I usually maintain an average speed of about 20 km/h during my rides, in this case it was enough for me to set the auto lap to a distance of about 650 m to keep the gauge alive on the watch display.

Another workaround is to use the Auto Scroll funvion to Sets the watch to scroll through all of the activity data screens automatically 

That is a very good tip, might really help as a workaround.

BTW, I will contact support.garmin.com now and complain, that they broke an essential core function of the RTL 515/516. Will point them to this thread and this one:
https://forums.garmin.com/beta-program/forerunner-955-series/public-beta-bug-reports/i/public-beta-version-20-xx/radar-missing-gauge-most-of-the-time-bike

In my opinion, the product does not work any longer as advertised and documented, which is not just a minor error.

Please all, consider to do the same and ask for fix or refund, to apply some pressure to Garmin.