Some Blocks Containing Data (Command, Chests), Regular Block (placements), Entities, Reverting to State Before Last Save

I had just finished creating a command block based vanilla fishing net design, when opening the world the next day (today) I noticed some things were off. The first thing I noticed was that cod were in the small space of water I created. These should not have been there, since I decided the system would not include cod very early on. Secondly, upon testing the "net" by throwing it in the water, the armor stands used were visible (should not have been) and noticeably missing tags and armor they acquired previously through the summon command. (some looking around later) When I went into the command blocks, I noticed that the commands, all 4 of them, had reverted back to when I was testing them early on. Next, I went to check a double chest I filled with old NBT+ command blocks, and some other copied and spare items. The chest was empty, and the items I had put in before were back in my inventory. Strangely, when looking at the latest and most recently placed command blocks, I noticed they were just as I had left them; fully updated. I checked to make sure this was not and issue with specifically chunks not saving right. After some analysis, I found that this was not chunk related. (proof is altered commands in one chunk and empty (altered) chest with untouched commands in another) As stated previously, this affects entities, blocks with data, and actual block placements. This also affected my inventory (like I never put the items in the chest), but again, strangely left some command blocks untouched. In other words, the affected entities (including the player), blocks (w/, w/o data) do not have a pattern to them or connecting them. I have including a couple screenshots as reference.

It was very frustrating to realize what had happened to my commands since the ones that were most difficult to fix were ruined.

I have not ever experienced a problem like this before.

Also worth noting that I have never modded Minecraft; it is vanilla 1.13.

 

Let me know if there is any more information that would be helpful in understanding the issue.