I love using iZotope RX Loudness Control in Avid.  Just mix your audio to your liking and then at the end, mix down your audio to stereo and throw on Loudness Control.  Then select your standard:  ATSC A, 85 in my case and render the effect.  It sets your overall level (usually just by a little bit -- I get it pretty close without it).  It's been super dependable and my broadcast client is happy.  UNTIL, MY LAST TWO PROJECTS.  WHERE IT ADDS A RANDOM HIT IN THE AUDIO.

How do I fix this issue?  I need it for a project that's airing this weekend and I need it to be reliable again.  Thanks!

Having your system specs would be helpful in helping here.  That aside, as a "Hail Mary", I would create a new user and then try the render.  User settings get corrupted and really odd things can happen after that.  A wild guess, but easy to try.

Jef