Once you click, and thereby filter, on the network timeline overview, I cannot find a way to undo the filtering.
When double clicking, it increases the filter to all, but subsequent requests won't be shown, as the filter is not removed, it is just moved to the newest time at the moment of double clicking.
Closing and opening the DevTools, or clearing the network tab, are the only ways I found so far (apart from increasing the filter everytime I need to see the newest requests), but keeping the request log without any timeline filtering is the goal.