The bug

Functions only consider the value of the gamerule maxCommandChainLength when the function starts, but should ignore any changes to it while the commands are running, see MC-124447.

However, this is not the case when a nested function is executed. In this case the length of the queued commands is compared with the current maxCommandChainLength value.

How to reproduce

1. Download the attached datapack MC-143266.zip and place it in the datapacks folder of your world
2. Run the function test:run_nested

   /function test:run_nested
   

   → It did not run any of the commands from the test:nested function; you can slightly increase the value set for maxCommandChainLength in test:run_nested and the nested function will be executed

Code analysis

See net.minecraft.advancements.FunctionManager.execute(FunctionObject, CommandSource) (MCP name)

Solution: The maxCommandChainLength value could be stored in a field when the execution of a function starts and then the value of the field can be used for nested functions.