HI
it is not possible to lock a clip. Yo can only lock tracks (along with its attached audio). Locked tracks show a hatched pattern along their length and attempting to move a clip or image onto a locked track cannot be done. If tracks are not locked or clips are not grouped,you should be able to grab any clip or image and drag it to an upper track or the same track or to a join between two other clips or insert into another image or clip. This action leaves a gap in the position where it was displaced from. So if this is not happening not sure why.
Try a test with a couple of tracks set up with clips and images and see if it still happens. If it works OK then you have some configuration in the project that is different to the test. Without seeing the faulty project it's difficult to know what is wrong. What version of VP are you using?
Try saving your project using..Save Portable Project As from the Menu/File. This option creates a folder containing all the files needed for someone to assemble it and take a look. Upload the folder to Google drive or similar hosting site, make it public and post the link to it to this forum. The instructions for doing this are at the top of this forum here.....
https://nch.invisionzone.com/topic/23659-share-a-screenshot-or-project-get-help/
Nat