I created a command block contraption in my world and when I opened the world, the testfor command in the command block said there was an error in the command, but it worked in the version 1.12.2
What I expected to happen was...
For the testfor command to find me (the player) and continue on the commands.
What actually happened was..
The command couldn't find me and the output line in the command block said there was an error in my command.
Steps to Reproduce
1. Get Command Block.
2. Type in the command (this is what I put in that worked in other versions(testfor @p[x=2125,y=54,z=-695,r=1])
3. When standing in the correct position, then opening up the command block, notice it shows the error message.
That command got removed in favor of execute if entity.