top fails to show busy process

i've had top running since yesterday evening as root in one workspace. in another i just started tar and xz to compress a few iso files to see how much space that might save. the top that was running already (updating every 20 seconds) was not showing these new processes. starting a new top did show them. i ran three concurrent instances of them (to test this) and they did not get shown, either. tar and xz were running as user phil while top was running as user root.

i left the bad top running. no upgrades have run since before i reboot yesterday evening. i am curious what might have gone wrong with top. any ideas what to check? the new run of top has exactly the same options as the bad one (top -d40).

maybe top is just spinning down?

i'll leave that bad process running for a while in case anyone has an idea of something to check. it did show some ffmpeg processes i ran last night converting some mp4 video files to webm format.