Had a bit of a search, but not seen anyone else posting about the same thing, so asking the question as I've had the same fault on both rear calipers now.

First time, I put the electric parking brake on then when I next went to drive away the drivers side actuator had failed and was stuck on. On closer inspection one of the lugs on the motor actuator casing had split and broken off, the casing which is plastic had split and the splined shaft wouldn't engage. Bought a complete new caliper to replace that one and now the exact same thing has happened on the passenger side, but this time it is stuck in the off position.

Anyone else had this problem? 2014 L494 HSE

Yes mine stuck on with the same problem replaced both they’re less than £100 each on eBay
https://www.rrsport.co.uk/forum/topic59153.html 2015 RRS DIESEL HYBRID

Very, very common, just be sure to get the correct motor as they are model year dependant, either 2 wire or 3 wire, the earlier 3 wire part contains a temp sensor.

I’ve had both of mine replaced under warranty with cracked casings Joined the X5 45e club
1994 Defender 90 300 tdi