The result of git bisect is the following commit:

commit 094fcf62d289f19a4633275812e9e5e500463e91
Author: Alan Third <alan@idiocy.org>
Date: Mon Oct 29 15:37:35 2018 +0000

Fix more drawing bugs in NS port (bug#32932)

* src/nsterm.m (ns_row_rect): New function.
(ns_clip_to_row): Remove function.
(ns_copy_bits): Fix mistake.
(ns_shift_glyphs_for_insert): Mark the frame as dirty instead of
directly copying.
(ns_draw_fringe_bitmap): Stop using ns_clip_to_row.
(ns_draw_window_cursor): Stop using ns_clip_to_row and perform a
display when not in redisplay.
(ns_update_window_begin): Remove redundant code that never executes.
([EmacsView drawRect:]): Show the rectangle being exposed in NSTRACE.
* src/xdisp.c (expose_window_tree) [HAVE_NS]:
(expose_frame) [HAVE_NS]: Redraw even if the frame is garbaged.