I've got an older world that I've had for years and have brought with me through multiple versions. I haven't played since 1.10 or so, and today I imported the world into 1.13.1. The world is survival, but I used cheats to add command blocks where I needed them. Now the command blocks don't work.
The command block is clocked, and is being activated. I can set the block command to
say "hi" and it will repeatedly say "hi" and output a redstone signal to its output comparator. But if I change the command back to what it originally was set to (
testfor @p[r=2]), I get an error message in the previous output which says
If I type the command into the console, I get an unknown command error. Furthermore, the command as written in the command block field is red, and
testfor does not autocomplete.