C1 varies only if RXLEV varies.
The RXLEV is from the BCCH frequency.
Due to multipath and measurement process, it is possible that RXLEV varies with a range of -6dB to +6dB.
In other words, the C1 shows variations of -6 to +6… but that’s normal.
Much more than this means there might be a hardware issue on the TRX1.
Or it might mean you are in a highly reflective terrain, with lots of multi-path and lots of fast fading.