I among many many others have had this problem for some time. It's completely random, it sometimes comes at 1% render and sometimes after 99%, or any place in between.
I've been on support chat like ten times, and had the senior team call me about five times, I've done everything they suggested (they often suggest the same thing although I try to explain that I've already tried it), so finally I gave up on support and spent a couple of days trying to figure it out myself.
What I found out, that works 100% for me, is going back to an older version of Media Encoder. The new fast hardware accelerated rendering was introduced in version 14.2. Using the Windows Task Manager, I noticed that version 14.2, 14.3 and 14.4 uses both CPU & GPU. What's a little strange is that it uses about 90% CPU & about 10% GPU. From version 14.5 and onward, Media Encoder uses about 30% CPU and 45% GPU, and it's from this version and up that the rendering fails.
I don't have a good explantion to why this is happening, but if you uninstall your Media Encoder and use 14.2, 14.3 or 14.4, rendering will work!
My 4K 50fps project that is 1h10 mins is estimated to take 1h to render with latest version of Media Encoder if it doesn't fail, which it does every single time. Using one of the older versions of Media Encoder the same render takes about 1h20 mins. When turning hardware acceleration off, which also gives 100% success rate to rendering, rendering of the same project takes about 6 hours!
It's not optimal, but change to an older version of Media Encoder, and rendering will work and speed will be decent.
Crash, Error or problem, Export, Hardware or GPU, How to, Performance
From version 14.5 and onward, Media Encoder uses about 30% CPU and 45% GPU, and it's from this version and up that the rendering fails. - v14.5 introduced support for hardware accelerated decoding for Nvidia/AMD GPUs, so that's most likely source of the issue in your case.