Fred
Apologies - I started this response last night and got a Blue Screen of Death and I figured it was my PC telling me "Enough" for the day (maybe my wife is training it or something ...) and I lost the response I had drafted and ran out of time - so here goes again.
There are two areas in TBC where you have settings on Images / image handling that are likely the cause of the issue that you are seeing. I imported the 2x images OK into TBC myself and they seemed to work just fine, however I think this depends on your settings somewhat.
1) After import, the settings are established, so you have to look at the properties of the Image. Find the image in Project Explorer under Imported Files. Select the image and look at its properties. The issue you are seeing is likely one of two things. First the View Priority - the higher the number the higher the priority the image has when two things overlap. If your images overlap, then set one image to a Higher View priority than the other. Secondly, when a software writes an image file, the area around the image to fill out the rectangle is painted in a color - typically white or Black and there should be a Transparency setting with the image that sets that color to Transparent - sometimes we get images where that is not set and you get the White Background (Rectangle around the image set to White or Black) that blocks out other images in the set - You can change that setting in the Properties for which color is the background color and it's Transparency. That will likely fix the issue you are seeing. (Transparent Background (Yes) and Transparent Pixel Color (Black or White (Typically at least)). These settings are available when you use Tiling, but not when you use No Tiling and Downsize the Images
2) On import of Images - we use the Settings that are found under Support - Options - Images and there you can manage images that come in from Station Set Ups (e.g. from SX10) and from Georeferenced Images. Here you can decide to Tile (for faster multiple resolution viewing) and to Downsize (to reduce the resolution of the images for faster working when handling large images at high resolution). You can also determine how to manage the Background Transparency (Set Pixel Transparency on Import and then select the color of Pixel to Black or White). This should fix the issues on Import of images. Once imported revert to option 1 above.
I am almost 100% certain that the above is your issue - let me know if not and send me screen grabs of these settings panes for each photo properties and the Support Options Dialog
The other challenge with these images is that they are great images and extremely high resolution - and while downsizing may not be what you want to do with them - I downsized to 2048x2048 and the res was still good and the display speed was much faster. You can do this on the fly and it will re process the images as requested and update the graphics
Alan