i connected the radar to a combinator clock slowly counting up so it will increase the radius over time until the combinator clock reaches a set limit (my was 60) and then reset to 10 and start counting up again.
this works for the first cycle, but it seems the radar can never decrease its settings atleast for near and far range limit. it seems it can only increase so it only starts scanning again if the n and f values are the same or greater than the biggest value the radar has received so far.

ps: i was able to reproduce this behaviour by only using constant combinators, it seems i never can go back to lower values without deconstructing the radar and to place (and connect a new one)

I have seen no issues using smaller values after larger. There is a forced far radius of near + 1, if n is greater than r or f
Can you post a screenshot of the signals in use and the misbehavior?

i tried it again, at first it was seemingly working fine. but it glitched out again, especially after scanning big areas in a very short time. then it did nothing for 5 minutes, then it started scanning again.

edit: so after some more testing, it seems only to happen when i lower the values exactly to the same time when the radar is scanning big amounts of black areas and the scanning process is slowed down very noticeably because of that.

https://imgur.com/a/EFJnWoO

When the game is generating new data there is can be a very large delay between when a script requests that a chunk is charted and when it actually is displayed. I suspect that this is the cause of the symptoms you are experiencing.