Hi lookandbuyme,
We have since received a few cases (including the one filed by itsjustme) in which thumbnail images for some items are not showing up on the Active Listings page and our engineering team is currently looking into those reports. It does not appear to be very widespread at the moment though.
I do not know enough about the cause of the problem at this point to tell you whether you may be impacted by it, but I don't personally feel this is something that you need to let keep you from posting new items to eBay.
If you do encounter this problem with any of your listings, please let us know by filing a support case and we will look into it further.
Also, I also feel that the thumbnail images within your account are taking an unusually long time to load so I have asked out engineering team to look into that behavior as well. Thanks for taking the time to mention that to us.
-Mike