Ad Not Delivery After Removing and Re-Adding Keyword

[jimpoo]

I had a keyword done very well on CTR.
Since google sent a lot of "expanded match" clicks, I removed this keyword three days ago, but I found the traffic dropped a lot, so I re-added the same keyword into my adgroup, the problem is that after two days, Google is still not delivery my ad on this keyword fully, although the 'Ads Diagnostic Tool' checking said it is ok.

I'm confused why does the same keyword not being treated the same as it used to be.

Anyone has this kind of experiences?

[jimpoo]

I went to check my adwords account this morning, notice that the re-adding keyword has 0 click on 360 impression.
I'm very stranged why it did gain a decent CTR before, but after I remove it and re-add it, the CTR go to hell.

Also, When I use 'Ads Diagnostic Tool' to check the keyword, it show me the following message:

What does this mean?
Your ad is not being shown for reasons unknown to the Ads Diagnostic Tool.

What can I do?
Our engineers have been notified of this problem with the Ads Diagnostic Tool and we are working to resolve the issue as soon as possible. We apologize for any inconvenience and appreciate your patience.