Exact same issue as here except it can now be reproduced in the normal Roblox client.
Only certain experiences appear to be affected, if in an affected experience (I linked one in the private message), simply do the following to reproduce:
Open the CoreGui
Wait a few seconds
Close the CoreGui via any means
Attempt to open your CoreGui again, observe that nothing happens.
System Info: CPU: Intel(R) Core™ i5-8400 CPU @ 2.80GHz GPU: NVIDIA GeForce GTX 1050 Memory: 16GB