I do 99% of my Rumble watching on a computer and use J K L and space to <<, >>, and pause.
So a few weeks ago I replaced my old Dell touchscreen AIO desktop with an Asus NUC and 27" monitor and I noticed J & L weren't working as expected. A few days later they were, and then again not. So I noticed working/not-working in intervals of me fat fingering the keyboard and just now deduced it down to if Caps is on, Rumble is cap sensitive and only accepts them lower case.
The wireless keyboard I use doesn't have a caps lock led, trying it on my laptop clued me in on this. At first I'd thought it was Shift + Caps... WTF?! But nope, just Caps.
It also could just be Windows 11, but the transition from a touchscreen to non-touch took me several days of trying to touch the monitor and realizing that doesn't work anymore lol
It's a free option, they throttle all the time and probably don't have their best equipment on it.