I found this on a German website: LG-OLED-TVs B9, C9, E9 und W9: Fix für Dolby Vision in Arbeit
I have no idea how credible they are. In part, from Google Translate:
Since the beginning of June, LG has been distributing firmware version 05.10.04 for OLED televisions of the 2019 generation, i.e. for the B9, C9, E9 and W9 series. The firmware causes an error in interaction with AV receivers, connected players and the HDR format Dolby Vision, which leads to strong image flickering.
When asked by heise online, LG stated that the error is known and that another firmware update for the affected OLED TVs with a fix is expected to appear next Monday, June 28, 2021.