When function tags are in a particular configuration, certain functions don't run when you would expect them to. I attached a data pack with the least amount of files needed to reproduce. This configuration has 2 function tags and 2 functions. When loaded it is to print two messages in chat, however the observed behavior is that only b:load runs.
It depends on the names of the tags and functions whether or not the bug will happen!
For example, renaming #c:a to either #c:load, #minecraft:a or #a:load will not cause this bug!
- Download the attached data pack mc-201840.zip and install it in a world
- Run /reload
- Observe that only "load B" is printed
- Do one of the following actions
- Replace "required": false with "required": true
- Rename #c:a to #c:load (and update reference in #minecraft:load
- Observe that both "load A" and "load B" are printed