I also have issues with 0.8.57
I downloaded this EPUB
https://www.mobileread.com/forums/showthread.php?t=35443 which has a minor error in its metadata (Author set as "Karl & May" when it should be "Karl May"). Editing the metadata and pressing the OK button, Calibre hangs. It uses 100% CPU and memory usage keeps on growing (hundreds of MB for a simple metadata change). Unfortunately I have tons of RAM in this machine so it would take hours for it to actually crash and print a trace due to memory allocation errors.
Anyone have the same issue?