For CC2531 coordinator and two routers with only Xiaomi devices (around 30) there have been at least four occasions in 6 months where I had to reflash one of the routers as it did not connect anymore (not the same device). I did not had to reflash the devices connected to that node, though.
After migrating to CC26X2R1 (and removing the routers) there was not a single issue.
Pairing of devices with CC2531 had to be done at less than one meter (and some times failing) while with CC26X2R1 it went through 3 walls on the first try.
Connection quality is also significantly improved (above 80 for most devices), while with CC2531 it was even less than 10 through one wall.