Hotkeys stop working after at some point

[zszabo2000]

(IMPORTANT) UPDATE: I neglected to mention two important facts:

1. I have a dual display setup -- an Alienware 17 notebook with built-in standard 1080P/60Hz LCD, as well as a Dell UP3214Q 4K display connected via DP. The 4K display, while secondary, is set as the main display in Windows 10.
2. Strangely, it doesn't think the built-in notebook LCD supports DDC (I've already known for a long time that it does, since other tools like ClickMonitorDDC recognize it as such). I don't have a driver for the panel (lp173wf4), so it shows up as "Generic" -- maybe that's got something to do with it. Anyway the important thing is that it shows up first in tB's list and tB seems to default to it, even after I select the other monitor from the list and change its brightness. In fact, if it does switch to, what it thinks is a "non DDC-compliant" display automatically (for whatever reason), then it certainly makes sense that the brightness controls would no longer work. The brightness controls are also not visible when I click the tB icon in the toolbox (or whatever; bottom right). For example, just now I clicked it again after changing the monitor over to the Dell a few minutes ago and the brightness slider was still visible -- so tB had not (yet?) switched back to the unsupported generic. I will try to remember to check again after a while (first hotkeys, then the slider) and report if I noticed that it definitely changed over on its own.

-- ORIGINAL BUG REPORT -- I'm not sure if it's after a certain period or due to a certain event (I only started using this a few days ago and just concluded that this is systematic -- see new para.). UPDATE(S): See below.

Regardless of specific hotkey settings (ctrl_shift_+/- by default; I set this to alt_shift... and the behavior remained exactly the same), with the program running in the background I have found.

1. UPDATE: I have now found that this is the case when the settings panel of tB is not open.
2. UPDATE2: I have furthermore found that this remains true even if the settings panel of tB is open, but the "hotkeys" tab has not been accessed yet.
3. UPDATE3: I have also found that the hotkeys start working once the hotkey tab has been activated (but no changes have been made). The hotkeys continue to work after that, even if the window is backgrounded or closed.
4. UPDATE4: Lastly, I have found that the hotkeys stop working some time after the window was closed. I remain ignorant regarding the specific cause of this (see above).