Make spacebar/down arrow work consistently

I mostly use voyager on a laptop, where I would like to scroll using spacebar or down arrow. It's not consistent though. I usually have to click somewhere on the page (which has the unfortunate effect of collapsing whatever comment I'm near), then spacebar/down arrow will work for "a while" ... not sure what's stopping it, but it does stop, then i have to click again (and collapse another comment), then they work for a bit...

If it's possible, please make it work consistently! Thanks!