It says resolved but I am still getting the problem as of 20w22a. I am working on a very large scale project and there are about 400 repeating command blocks and I am near about 250 at a time. I have to open the command block about 13-56 times for it to load the command inside. I also noted that when there are even more command blocks some other command blocks fully stop working even though they are always active. This might just be because the commands are not loaded, or a separate bug.
In the video I added to the attachments you can see that if I click "Done" or the enter button it saves as having no command. But if I keep clicking cancel to load up the command or re-typing the command over and over eventually it will keep working.