Scan Dll slow down program start

Hi All,
I have been using Avast free anti-virus for several years. I don’t know from which version, it slows down all the program start.
I found that Avast will scan the .dll everytime I execute the same program. For example, I start excel, and close it, and start again, it takes a long time, which it doesn’t make sense.

Then I try to untick “Scan Libraries (DLLS) when loading”, everything become normal. I am quite curious whether the “Use Transient caching” setting is working or not. I think the program is slow in first start that make sense, but why the program still slow start for the next time. My PC is i7 + 32G ram so I don’t think it is hardware problem.
Is there any way to fix it?
Michael