Loosing images in Lightroom classic

This is a weird one, so pay attention. Not sure if anyone else has seen this issue.

I have my catalog and images on an external portable hard drive. This is because I will often shoot away from home and I want the ability use my laptop to either shoot tethered or offload and review my photos before returning home. I typically don't do much editing on the laptop because I prefer my home PC with larger calibrated monitor. I have used this method for years with no issues.

However, recently when I plug the portable hard drive back into my home PC after travelling, any images taken since the last time the catalog was opened at home are not in the catalog and often have been removed from the portable hard-drive. Fortunately I am religious about backing up all images, so I haven't actually lost any photos yet, but I do lose any edits or flagging/rating I may have done.

What is also weird is I set Lightroom to backup every time I exit. This weekend I was travelling and took a large number of photos, many done while tethered to my laptop. I have three backup files from the weekend, one from Saturday and two from Sunday. When the images did not show in the catalog when I opened it, I restored the catalog from each of the back-ups and none of them contained the images either.

I need to find out what is going on and how to fix it so I don't lose this information and cause myself hours of extra work re-importing the images to the catalog and redoing all of the work I had done previously. 

Many of the images from this weekend I had the client review and mark which ones he wanted. All of that is now lost. Any help would be appreciated.