Switched to 2017, and ever since I've been having mates disappear.

I'll drop completely new parts into an assembly, mate them together with standard mates, ok out of the mate menu, and change my view orientation.

I'll grab one of the parts that I just dropped in, and it's mated to nothing, even thought I just dropped half a dozen mates on it.

I've not been able to make this happen on demand, but it is happening frequently. Mates have disappeared several times this morning already. A coworker is having a similar problem with his assemblies.

We're not working with multi configuration assemblies. The mates aren't suppressed, they're just gone.  I've rebooted several times since I first noticed that this was happening.

How often is this happening to you, and what have you found helps alleviate this?