Narcissistic staff member returning

[Newyorklady]

So I have a member of staff I manage returning to work within the next 2 weeks from a short career break.
I am dreading it because he is a narcissist.
He fluctuates between telling me (and others) I am the best Manager he’s ever had (all charm and smiles) to me then finding out he’s been sabotaging me behind my back. Gossip, backstabbing, maligning.
This varies between subtler maligning me to others (in a crafty way) to out right confronting me when he doesn’t get his own way.
Massive ego (tells me he’s the best staff member I have which is so untrue) then down tools as protests when under slight pressure.
He’s awful. I hate dealing with him. I’ve tried the grey rock effect (lasts for about 2 months until a decision does not go his way) to trying to massage ego by praising when he works well, to addressing behaviour. No matter what I try always ends up with me finding out he’s been very negative about me, the organisation, the work etc etc.
He has no filter at the time and this has lead to him being negative to our customers.
Im thinking of changing my approach now (as behaviours will rear ugly head soon enough) to outlining expectations and dealing with behaviour head on. I record everything.
Return after career break meeting turned ugly when I informed him I needed to see a. Improvement in his behaviour m. This suddenly turned into a personal attack on myself. I was this, that, the other. Called me a liar etc.
After 2 years of this my previous strategies have not worked.
Any advice ?
For context each staff member has told me they are dreading him returning.
A lot of the behaviour is sly and underhand.

Why has he not been sacked already?

I wouldn't put up with a shithead like him in my organisation.

Unfortunately not enough solid evidence. He’s very clever.
Though he has made mistakes recently by being negative to customers so we have that evidence.
My approach after return is to
log and address everything as previous approaches have not worked.
If this was private industry he would be out by now.

Surely insubordination and failure to adhere to management requests, at a minimum, are gross misconduct grounds?

You need to brush up on your employer policies and assert yourself better and ensure you sack him otherwise nothing will change.

The way he “downs tools” is done very craftily.
So we have certain tasks that can take longer than others, so he will say they have taken him longer due to complexities so it’s hard to evidence but we know it’s happening.
In terms of insubordination, if I raise behaviour issues he will blatantly point the finger at my management and say it’s me.
I have tried escalating and was about to start processes when he went in carer break.

While the downing tools is hard to evidence, and I agree, behaviour issues are not.

Let him point to your management style - without evidence you are troubling him, he has no grounds to stand on.

YOU DO.

Document his every word/action/time/date/location and slap that dossier in front of him and HR.

His feet wont touch. You need to discover your backbone, otherwise nothing will change because that toxic employee certainly wont.

I worked with one and whatever we said or did always had a counter. We ended up getting rid of the person through redundancy because yes they were very clever at manipulation and putting negative optics on others. That was the only thing that worked.