D4 VEA 'add 0.5L' oil level warning

[Zebster]

Shortly after starting a short journey home last night a message popped up to tell me that I needed to add 0.5L of engine oil. I continued home, parked up and turned off, however then realised that I should have parked on a more level location to enable use of the electronic level check. So I immediately restarted the car and moved it; surprisingly the warning message had gone (I did scroll through the messages to check). I then left the car overnight.

This morning I've been out to check the level but - although the level display outline is available - there is no actual level indication shown on the gauge... so now I'm not sure if the electronic dipstick is working OK? I started the engine and just moved the car a few metres and there were no warning messages.

Oil was last changed by a Volvo dealer about 2k miles ago and I last checked the oil level about 1k miles ago (when the electronic level indicated around 75/80%, which is about what I expected). No obvious signs of leakage in the engine bay nor on the ground where the car is usually parked overnight. Car has now done 73k miles.

I do have a litre of the correct spec oil (Shell 0w20 VCC RBS0-2AE) so I could easily add some, however I've read a few forum posts where owners in a similar position have ended up over-filling. I have carefully studied the owner's manual, but does anyone have any useful experience with this issue? I'm currently tempted to add just 0.25L (rather than the total 0.5L in one go), take it for the minimum '30km drive' then park up for a couple of hours and try the electronic gauge again.

TIA