Try this: (1) Lock the screen via the Apple menu; (2) press the escape key to make the Lock Screen go black; (3) press the space bar. Does the Lock Screen appear again?

If not, try pressing one of the brightness keys (increase or decrease) to make the Lock Screen appear again.

If you don’t encounter a bug, try pressing the escape key again then the space bar to bring back the Lock Screen.

Repeat this several times to see if the bug occurs for you.