Never hurts to reset the device just in case that helps.
Confirm that the Sort Artist fields for the affected tracks are actually empty instead of containing one or more invisible spaces. Note that iTunes groups on Album Artist (order amended by Sort Album Artist) whereas the iPod Classic groups on Artist (order amended by Sort Artist).
See the section Missing or Artist or Album not with others by same artist which explains that enabling one or both of Settings > Main Menu > Compilations or Settings > Music Menu > Compilations can affect where tracks appear in cover flow.
The iTunes Store tends to mark albums that include any featured artists, or form an anthology of an artist's work, as part of a compilation to mitigate some of iTunes historically poor track grouping issues. Depending on your preferences within iTunes this flag may not have any noticable effect in iTunes, but may control what happens on the device.
Even though you can't see where the problem lies it may help to amend the track details in the way I describe at Tried that, there are STILL too many covers and then resync the device.
tt2