Whenever my HP laptop with Elementary OS 5 Juno goes into suspend, either due to it being left alone for a while or closing the lid, when I come back and log in, the screen brightness is dimmed to about 50%, regardless of what it was set to before. If I then increase the brightness, it adds to the previous brightness and the display lightens up. So it seems like a caching issue to me.
To clarify: Let's say I set my brightness to 75%. I suspend the machine, come back, it looks like it's at 50%. I log in and it stays dim. I press the button to increase the brightness once and the brightness is now at 80% and the screen now also reflects this brightness correctly.
Of course it's difficult for me to reproduce this, since I don't have access to other machines with Elementary. I would appreciate feedback on whether you can provoke this problem on your machine.