yes it is a usual operation during LAU.
to reduce those radio ping pongs between LAC, you could increase the Cell Reselect Hysteresis (CRH) up to 16dB on both cells.
Your scenario is quite extreme. The duration of a LAU is so short that it’s really bad luck if the MS is changing LAC while NSS is trying to page it. It’s really a matter of few seconds.
The only thing is to avoid ping pong LAU, for sure.
CRH is a good thing. Try also increase TO and PT (temp offset, penalty time), to values 4 (40dB) and 3 (40s) for example, that’s enough to avoid stupid reselections.