The (at the time of writing) newest patch of the game, 5.05, added a bunch of new features that ended up being buggy and they grant unfair advantages, such as:

• the encounter rate not being adjusted to account for running (so you would get half as many encounters)
• Toriel running through the Outlands at double speed
• Muffet Skip not working under most conditions
• ... and probably more.

So, we decided to disallow this patch for speedruns. If you want to submit runs, you're going to have to either play on an older version, wait for a new update OR use a custom version of 5.05 that fixes these bugs, which can be found here.

Tutorial on how to apply this modified patch:

1. Download the original 5.05
2. Download and open DeltaPatcher
3. In the "Original file" section, add your app.asar file found in the game's folder -> resources (if you want to keep the vanilla version around for any reason, make a copy of this file)
4. In the "XDelta patch" section, add the newly downloaded file (505fix_67341b6c.xdelta)
5. Press "Apply patch".