Adjusting flex markers/bug

I'd just like to point out that this is my first post to this forum, first and foremost! 

I've used Flex Time many times in the past but I now receive the following bug, and I cannot figure out the source or how it even started. I have a recording of a drumset with 10 audio tracks, grouped together with phase-locked editing mode engaged. The song itself is about 9 minutes long. I have comped and mixed the drums. I am now editing the timing via Flex Mode(Slicing) and every time I move a flex marker, Logic gives me the pinwheel and it loads for 10 seconds, which is excruciatingly slow for the amount of edits I have to do; in fact at this rate it'll be hours of merely moving flex markers around! This never used to have to "load" every time I move a marker, so there's definitely something weird happening.

I've tried removing all plugins for the tracks, freeze mode is off, all the drum regions are flattened and merged, I've tried splitting the region into a short segment and adjusting the flex markers to no avail, I've tried creating a brand new project and importing the drum tracks and their content(via media browser), and I've even tried recording the output of just the "kick in" track, bussed to a new audio track and using flex time on that, to no avail. 

I am using a 2013 Mac Pro, 6 core, 256 SSD drive. 

The projects are stored on a 10,800rpm G-Drive harddrive. 

OSX version 10.10.5. Logic version 10.2.2.

Thanks for any help.

I have not tried to do what you describe, but from what it reads like, I'm guessing that Logic app is taking some time to cache (read/write) info from all of the drum audio files, e.g., transient markers are being moved for all the locked tracks,  This apple tech note,

https://support.apple.com/en-us/HT201943

- seems to indicate that you have to pick a SINGLE track as the Q reference, and you adjust the transients for that track (and all the other tracks  follow).  Now maybe that still takes too much time to cache anyway for some reason.  But maybe worthwhile to at least try what the tech note describes if you have not done so.

Thanks for the suggestion and the link. This is actually the same guide I followed for my current method of using flex time.

I did manage to solve my problem. Although the regions I was adjusting flex markers on were already flattened and merged, there were some other regions on the same track(later in the song) that were not, and had probably about 20 different "takes" for each of the drum tracks within the group. After I merely flattened and merged those(even though I did not adjust any flex markers on those), the issue of the loading time is now gone!

I hope someone else who has this problem is able to find this post.