I just noticed this behavior yesterday. One of the things I most appreciate about these forums is that they're filled with people who have the great qualities of being very intelligent, nice, and eager to help. I see them here in this thread. Thanks for the work you've already done investigating this issue. I'll see what the suggested fixes do for me.
For what it's worth, I'm also uncomfortable with the security downgrade that results if the corresponding suggested fix does improve performance of the Mac App Store on one's machine.
(Just to be clear: I have no problem with the suggested fix, +per se+ —thanks, in fact, and good work tracking that down—but rather that Apple (I think indirectly, to be fair) created this problem where some have to choose between better security on the one hand, and a usable MAS on the other.)
My meager contribution is aimed at anyone reading this thread that would place themselves more toward the "novice" end of the spectrum: if you have apps that become unresponsive, that beachball often, etc., you can do some simple detective work like I did.
First, in your Utilities folder, open up Activity Monitor and Console. To begin with, I'll usually click on the CPU column in Activity Monitor to sort descending, which will show the apps with the most CPU usage at the top.
In Console, I'll leave "All Messages" selected in the left-most Log List column, at least to begin with. If you don't see the vertical list of logs, click the "Show Log List" button in the toolbar.
Then I'll launch the app: MAS, in this case, but then immediately go to the dock and click on Console and Activity Monitor to watch what was going on.
Right away I saw the error messages in Console. I thought that "CGBitmapContextGetBitsPerComponent" would probably be a string that was specific to this problem, so I searched for that string, plus "Mac App Store", which brought me here: a thread with some possible fixes to try. I'm not a programmer, and I don't even know what "CGBitmapContextGetBitsPerComponent" is, but it's great that I could use it to locate some possible solutions.
I hope that helps someone. My apologies for the length.
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