> I have the same problem.
>
> $ xrdb -query
> emacs.font:	DejaVu Sans Mono-12
>
> (custom-set-faces
>  '(default ((t (:family "DejaVu Sans Mono" :foundry "PfEd" :slant normal :weight normal :height 120 :width normal)))))

These settings now cause such a strange effect that tabs have gigantic heights
on the tab-bar, while tab text still stays small.  Such sizes make sense only
when used with double scaling on a HiDPI display, but no scaling is really used
in this case: