Multiple devices failed at once

I recently returned from holiday to find that a number of my smartthings and home automation devices had all failed.
My motion sensor is completely dead - changing the battery (which was last reported at 67%) has done nothing and the LED never blinks or illuminates even when resetting (holding while inserting the battery).
My hue light-strip keeps getting reported as ‘unavailable’. I can work around this by turning off the device health toggle and back on. Its working fine other than that and working perfectly through the Hue app and Alexa.
One of my multi sensors has stopped working. Haven’t looked into this much but that too is listed as ‘unavailable’. I haven’t long changed the battery in this so doubt thats the cause.

Has anyone else seen this sort of systematic failure?
Had to happen while I was on holiday too so I had no visibility of the home while I was away! ARGH!