your toy computer is not a supported platform
look for any errors in browser console
e: the way i'm seeing your problem it's more likely a continuation of your previous label-related troubles.
i don't want to look this up right now but it's very likely that counters are being requested after the initial feed opens because that's how the startup always supposed to work, tree, initial feed, done. nowadays, many years and changes after, i guess those two load in parallel, oh well.
if your computer is really slow at generating the tree the counter request might happen too soon and the tree stays uninitialized until you do some counter-related operation i.e. the feed is updated or you mark something read.
as before re:labels i agree that this is suboptimal and promise to take a look at whether this is the reason and how to fix it
e: the interesting part is that i'm looking at the code right now and it still waits until the tree is loaded before proceeding any further and now i'm somewhat not sure why this even happens at all for you (that includes the label problem too btw).
yeah, even with a manual delay i can't reproduce those two loading out of sync.