M2E Pro set the mode of the images uploading to the Self-Hosted by default. It is caused by the number of advantages of this mode such as speed of running - it is not so much time-consuming comparing to the process of images uploading to the EPS Service.
Recently eBay implemented some changes which affected updating of the Items which have Self-Hosted images. Earlier while you were using the Self-Hosted mode, the images' links on eBay were identical to the original (vendors') links. But now, all the images you upload are redirected to the EPS service where their links are changed. Thus, the modified links are used on the eBay front-end.
Taking into account the fact, that there are no mechanisms which checks the changes of images placed under the particular link on eBay, the situation when the picture is changed but the URL is still the same does not allow updating the images on front-end even after the Revise is executed via M2E Pro.
Not-updated images on eBay front-end after the Revise is run for Self-Hosted images is not related to M2E Pro functionality, but to eBay Picture Service cache. So, when you run the Revise action after the picture was changed under the remain URL, M2E Pro sends the updated image. However, eBay does not verify the content for the link and thinks that there were no changes made. Thus, the image is not changed for this Item.
eBay help describe this issue in the Replacing Photo section.
As a possible solution, we suggest changing the image URL in Magento to make it be updated on eBay.
Please note, the EPS-Hosted mode is not recommended to be used as it may have a negative impact on the performance of your system. The synchronization process can become a very time-consuming.