Hi Afrizona,
I am not aware of any current technical issues that would explain why your are not seeing thumbnails for your listings that use externally hosted images when you look them up through mobile devices, so we would need to look into this further to reach a conclusion.
However, I just looked up one of your listings that is using externally hosted images as the Gallery images through both the eBay app and website on my iPad and I was able to see a thumbnail sized image on the search results page in both cases.
If you would like us to take a look at a specific example, just file a support case from under the “Help” tab within your account and provide us with all the relevant details and we will see if we can figure out what is happening in your case.
Specifically, it would be helpful to know one or two examples of listings for which you are seeing the behavior, which mobile devices you are using and which process you are using to reach the page that is not showing the thumbnails.
-Mike