I have the new vegas pro 19. I didnt mention it cause I said I updated it a few days ago to your latest version and I dont think you still make updates for older versions.

My rig is a custom build built by me. Been building my workstations since 1998.

CASE: CORSAIR OBSIDIAN 750D Full-Tower ATX Case - Airflow Edition
CPU: AMD Ryzen Threadripper 3970X 32-Core, 64-Thread Unlocked (5.0GHz)
AIO: Corsair iCUE H150i Elite.
MOBO: MSI Creator TRX40
RAM: XPG SPECTRIX D50 128GB (8x16GB) DDR4 4400Hz
GPU: XFX Speedster Radeon RX 6900 XT Ultra 16GB GDDR6
SSD: XPG GAMMIX S70 2TB (OS, Games & App's)
SSD: XPG GAMMIX S70 1TB (Recording)
HDD: Seagate Exos X18 18TB Enterprise (Storage)
BLURAY: Pioneer PIO-BDR-211UBK
KEYBOARD: HyperX Alloy Origins
MICE: Pulsefire Raid
HEAGSETS: AKG HSC271
SOUND CARD: Roland Octa-Capture
MONITOR: AOC CQ27G2 27" Curved, Frameless, 1ms, 144Hz 1440p
PSU: Corsair HXi Series 80+ Platinum Certified PSU

True, they (MAGIX/VEGAS) don't update older versions but a user is still able to update his/her previous build to the last build/update of that old version.

I just did more testing, and the problem is 100% with using AMD VCE. I left the same settings and used Mainconcept HVEC instead, and the video came out perfect. No audio sync problems. I'm assuming AMD VCE is for rendering with video card. Cause it went from rending very fast to very slow and cpu usage went from 30% to 93% or so. CPU rendering might be slow but less problematic, at least with Vegas pro. You guys need to fix something that might be affected by the new update. Cause I have rendered about 50 videos of more than an hour long with extensive editing in the past few months with the same setting and I've never seen the problem until now. This is going to be bad for me because I bought vegas pro 19 and built this system to make videos faster and going with cpu only, even tho it's a threadripper is always slower than gpu. I hope you guys can figure out what happened. I hope my testings help you out in some ways.

GOOD Rendering Settings

BAD Rendering Settings

Don't render hevc myself at that high of a bitrate with Vegas because my multi-hour shoots are between 60 and 135mbps. But I did notice general issues with amd driver versions on my 6900xt under Win11. Had problems with amd 21q3 till I switched to 21.10.2. Had similar problems after recent Win10 updates on a Radeon VII that went away after an update there from amd 21q3 to 21q4.

Another thing I noticed is that checking the 'hevc legacy' checkbox on the io tab dramatically improves render quality of hevc source material no matter which encoder is used. Render time is longer, however.

Also found the amd hq setting did little to nothing for render quality measured with ffmetrics. Saw a significant impact, however, changing the render quality to Best in project properties.

ok I've spent the entire morning troubleshooting and testing and what I found earlier is a somewhat a solution. But I hated that rendering was so slow. I thought why does it only do it when I render at 135-240mbps vbr? It never gives me problems with 50-135mbps vbr. I noticed I was using vbr peak constrain and I thought maybe when rendering to high quality and set to 30 fps audio goes off since its constrained to something that's desyncing the audio from video towards the end of a 20+ minute videos. I changed it to latency constraint instead and everything is 100% good. Not sure what it does but I am able to get the audio to work ok and I still have quality high. So, it wasnt the AMD VCE at all, or video card. Here is what I have now

I hope you guys understand what I went thru, and everything is clear now. Might not be the software problem at all. Might be that I was not supposed to go with peak constrain with such high-quality rendered video especially since it's only 30fps. Maybe, who knows? I majored on music and minor on SNR engineering. SO, this is new to me and I'm learning a lot since I understand pc building and how it works. But takes a lot of testing, troubleshooting to learn about a new DAW or editing software.

Anyway, thanks for the responds