This has been an issue that comes up for since at least version 7.1.9 where sometimes reflection probes will only render when the camera is inside of them then derender when the camera leave like it's getting culled. Most of the time I've run into it is from attaching probes to other items, take them then rerez then out but it wasnt always consist repro.

Testing out the latest version 7.2.1 I've seen this is still an issue and now I've found a location where a probe doesnt appear to be attached to anything else and its just a normal inworld object and so far is consistent in repro this problem.

Video showing issue.

The location is not my house but another users house so out of respect the location is in the Viewer Info section only.

UPDATE: Did more testing and wiped out cache and settings. On High preset for graphics I am able to reliably repro this even in the LL roads at the new Ridgewood exclave sims at the car rez parcels. http://maps.secondlife.com/secondlife/Tequila%20Rosa/103/154/26

Rez a prim

Set to reflection probe

Notice will derender when camera leave probe.

A few times I noticed setting max reflection probes to Ultra would cause probes to render as expected how ever as soon as I change the draw distance from 128 to 192 the same problem started happening again even when I reduced the draw distance back to the original value. In this area there is only about 2-3 reflection probes in a 1-2 region distance. Note that this issue has seen since before Max Reflection probe was implemented just not consistently repro.