When i tried to remove in 19w06a a bunch of glass with the fill command my game crashed and gave me a crash report. I tried it again and minecraft crashed again. So i had to do it all by hand. It was pretty frustrating. Please fix it- it sucks.
(Normaly the fill command works,but somehow it doesn't in 19w06a.)
Is the game freezing or does it give you a crash report? If it's the latter, please attach the crash report (.minecraft/crash-reports/crash-<DATE>-client.txt) here. If not, perhaps the command you are using is causing too many changes for your computer to handle. Can you also provide the command you are using?