Thoughts and suggestions on big scale Taboola’s campaigns?

I’m running ecom ads on Taboola for the past few months now. Spent well over $1M, had many ups and downs. I’m running on SmartBid – Optimized. However I am still struggling to create successful campaigns. There are still lots of questions I don’t have the answer for, although I’m testing new ideas every day. Here are a few of them:

• Blocking bad performing banners or adding new ones to an established campaign (70+ conversion pixel on the campaign, running for more than 3-4 days) seems to do more bad than good to the campaign. It usually changes performance quite a bit and almost always kills the campaign. Why could this happen and is there any way to prevent it from happening?
• Changing Site bid %s on an established campaign doesn’t do any good either when ...