I’ve done several flights today, and before I started I deleted the a320nx folder, and re-installed the latest Custom version ( I always do this as its updated more regularly).
I’m having a similar problem. As soon as I enter the STAR, I activate the approach on the MCDU, and then the speed drops to around 210 which is was i expect.
Then as soon as i hit flaps 1, after a few seconds the engines just gun straight up. After several flights I’ve come up with a workaround… go to Flaps 1 as normal, and if it happens, go straight to Flaps 2! This then settles it back down to normal.
I think this has already been reported on Github, so I will keep just hitting Flaps 2 until a fix has been put in place.