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. 

As I wrote in the beta bug's report, any "messages" written on the watch, like the one from "Training performance" or a Whatsapp's notification seem to reset a counter which then display the gauge for some time.

You're proposition with lap button is in this category too.

I have bissected lots of linux kernel to find bug and for someone with the source it's really a fast and easy task, I hope we got a fix.

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.

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.