Good testing. Nice to know before you go.
I am not seeing the elongation in the centre you mentioned except for one image which looks like guiding errors. The other last few images I assume are centre all look good. Just brighter stars.
FSQ106EDX111 was a bit hit or miss with sample scopes. I had one that had no issues (16803 corners were good). But there were a number of complaints on the Tak uncensored Yahoo Group.
Tak added a teflon pressure pad to reduce flex on one version (not sure it may've been the EDX111). A lot were fiddling with the pressure screws under the focuser to get rid of the flex with some good results.
The EDXiv removes the CAA and replaces it with a solid casting.
So you could try the tightening of the Tak focuser. I'd google for threads about this but basically its those small screws underneath the focuser.
Just out of interest did you know there was another version of the FSQ106EDX - its called the FSQ106EDP. Not sure what the differences are. I've seen it on a Japanese site - kyoei - Osaka:
Greg.
https://www.kyoei-osaka.jp/SHOP/taka...sq-106edp.html
Greg.