When working with large files if I didn't save in a while at some point this starts happening. I still had several GB of free RAM (6-8 GB free from 16 total). The transformation, be it free transform or liquify simply gets applies every few seconds, making working with it impossible. Saving the document helps usually, but sometimes Krita has to be closed and re-opened to free up RAM for the issue to go away. Steps to reproduce: 1; Open large canvas and do memory intensive operations (eg. painting with large brushes), but don't save. 2; Once Krita's memory usage goes up, try transforming. Issue is present for a while, I just kept forgetting to make a ticket. :(
*** This bug has been marked as a duplicate of bug 343790 ***