It seems you can define "the 4/3 problem" in various ways. But always
by doing something wrong! Because there is no real 4/3 problem, it is
just a paradox.
In this discussion, for instance, entry 14 makes clear that the paradox
can be formulated by ignoring that a moving charged sphere becomes an
ellipsoid, which of course is an error, so no wonder a paradox results:
If there is no real problem then of course we can ignore loaded
questions like "does the problem remain in QM?" as in stackexchange's
discussion, or "does the problem lie with [insert some fact]" as in
this thread. We can just say that there is no problem if we avoid
errors and if we do not avoid errors we can create the problem in a
number of different ways..