This exact thing happened to me, I was terraforming some mountains using the clone and fill commands, I changed the random tick speed to super high so the grass blocks would turn to dirt and they didn’t. I changed the tick speed back and the went back to terraforming the rest of the mountains while I waited. I was building a adventure map and decided to test something using invisibility, and when I gave myself invisibility nothing happened. I tried other commands and they didn’t work either. Even the command blocks I had placed and had previously put lots of very long commands in had been wiped. I tried typing more commands in and for some reason the done button as well as the other command block settings were unpressable, they where still there but they had a dark grey texture like a setting your not allowed to touch. I exited the world and when it said saving for five straight minutes I got worried. I clicked the x on the corner and it did nothing, so I decided to leave it and see if it could save. When I got back it had closed. I tried loading the world again and it had saved the changes until the commands stopped, and they still didn’t work. I broke my command blocks and tried again. This time I had to use program manager to close it. It also still didn’t work. I re booted my pc, fiddled with world settings, backups and nothing fixed the world. It’s still broken right now and I’d love an easy fix. I also tried leaving it as long as it needed. I wasn’t watching but eventually I was at the main menu, when I loaded the world it didn’t save. I suspect that if you are running a lot of commands and making a lot of changes really quickly It could break the saving for that world. I might be wrong but I’m not gonna use repeating command blocks for the fill command anymore. It didn’t seem to affect my other worlds. By the way I’m in mine craft 1.15 and the world this happened in was created in minecraft 1.15 so it hasn’t even had to be updated. I will post again if I find what happened or a potential fix
This exact thing happened to me, I was terraforming some mountains using the clone and fill commands, I changed the random tick speed to super high so the grass blocks would turn to dirt and they didn’t. I changed the tick speed back and the went back to terraforming the rest of the mountains while I waited. I was building a adventure map and decided to test something using invisibility, and when I gave myself invisibility nothing happened. I tried other commands and they didn’t work either. Even the command blocks I had placed and had previously put lots of very long commands in had been wiped. I tried typing more commands in and for some reason the done button as well as the other command block settings were unpressable, they where still there but they had a dark grey texture like a setting your not allowed to touch. I exited the world and when it said saving for five straight minutes I got worried. I clicked the x on the corner and it did nothing, so I decided to leave it and see if it could save. When I got back it had closed. I tried loading the world again and it had saved the changes until the commands stopped, and they still didn’t work. I broke my command blocks and tried again. This time I had to use program manager to close it. It also still didn’t work. I re booted my pc, fiddled with world settings, backups and nothing fixed the world. It’s still broken right now and I’d love an easy fix. I also tried leaving it as long as it needed. I wasn’t watching but eventually I was at the main menu, when I loaded the world it didn’t save. I suspect that if you are running a lot of commands and making a lot of changes really quickly It could break the saving for that world. I might be wrong but I’m not gonna use repeating command blocks for the fill command anymore. It didn’t seem to affect my other worlds. By the way I’m in mine craft 1.15 and the world this happened in was created in minecraft 1.15 so it hasn’t even had to be updated. I will post again if I find what happened or a potential fix