

It is a really disappointing, frustrating issue. If the adapter of your HDMI is still in warranty, then you can replace it or send it to the manufacturers for repair. Similarly, these solutions are used for solving USB-C to HDMI not working. Some users need to replace their HDMI adapters so that they can work properly. I've even had the SMC fail and had to reset it due to this issue, and it affects my work several times a month. The above solution will solve the issue of many users but not for all.
MY APPLE MAC HDMI ADAPTER NOT WORKING PC

It helped a bit to stop using the $300 Belkin dock I bought from apple for the Ultrafine, so it is only serving the third display - but issues abound.
MY APPLE MAC HDMI ADAPTER NOT WORKING PRO
I have had just terrible trouble with crashes as well on my brand new MacBook Pro this year, but connecting a LG Ultrafine and a Display Port (or HDMI via a DisplayPort → HDMI cable) display results in an unpredictable, crash-prone environment.
