Have you cut into any of your meat, pre-sear, just to see what level of doneness it's at from the sous vide?
The most common cause of over-cooked meat is that the sear is at too low of a temperature and too long in contact with the cooking surface. You want a good solid cast iron pan (and good ventilation! - searing produces a lot of smoke!)
If I want to produce the thinnest layer of char, preserving the doneness of my meat, I put my heat on full and don't put my avocado oil in the pan until the cast iron is already blistering hot and smoking. Then I put in my avocado oil, swirl it around (making sure it's piping hot), then I throw in about a tablespoon of butter which I lay the meat on (butter just produces a nice char and flavour).
With a pan this hot, leaving a surface of your meat stationary for a full minute will produce a blackened exterior - if you want less char, you need to keep it moving.
Lots of reference charts for smoke points of cooking oils out there, here's one:
That's the pinnacle of how shallow a sear you can do (the highest heat) - you could play with other oils and lower temperatures after that, but remember, if you're searing at a low temperature you can cook your meat all of the way through (with is really not the point of sous vide)
Getting back to the pre-sear question - do you have another good thermometer to make sure that the APC isn't malfunctioning? If not buy or borrow one (I have a Taylor digital instant thermometer I'm a fan of - quite inexpensive) and verify that it's accurate in it's moderation of your bath.
If you haven't already, you should familiarize yourself with the serious eats guide here:
But, you're right in the hunt for rare at 50C (49C is 120F - the food lab's recommendation for rare).
Let's presume you aren't trying for blue.