If you purchase the mechanic upgrades that lower the requirements for the sponsor objectives, they become permanently bugged.  Completed objectives will become uncompleted when you switch to a new sponsor.  AVAX, which was previously locked and unable to be completed, can now be completed.  However, it's become bugged for me, showing 2/3 objectives completed when in fact all objectives are checked off.
The new DLC sponsor objectives are pretty grind heavy as well. 
I will also warn you that at the end of an event, if you choose to restart the race, you can experience a complete wipe of all your sponsor objectives.  It completely freaks out your save file and brings the yellow exclamation mark back on everything you've unlocked too.  I manually back up my saves, so I was able to fix this, but I did some more testing and was able to replicate this bug.  I don't know if it was fixed, but this is just a heads up.
As for quality control, I suspect they are hard at work, but because of deadlines, budgets, and whatever other industry things going on within Codemasters and EA they may be facing a tough time.  This games needs some extensive bug fixing.  I have had fun with it, but I'm not going to lie...this is not the level of quality I expect Codemasters and I'm disappointed.