My pot grown acer had the same problem last year. Seeking advice,
I was told that acers are prone to leaf wind scorching and particularly
from the early morning sun.
I now keep it in dappled shade making sure the compost is damp,
and apart from a small attack of scale insects, all is well with it.

Roscoe
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"Debs" wrote in a message:
I have two Acers in pots, grown from germinated seeds some 13 years ago.
One Palmatum (red) the other Dissectum (lime green). Imagine my
horror when my palmatum started to wither and drop its leaves. The leaves
dry out from the tips backwards and eventually fall off although the stems
are still perfectly green. The decline started from the new growth and has
worked its way down to the oldest branches.