v2.3.0 introduced mutex locks and my custom merge function stuck

[BananZG]

Describe the bug
After upgrading to v2.3.0, I noticed that there's new mutex lock added to all the main functions.
I wanted to make sure that in my project, all keys are case insensitive (as i moved from Viper hehe), I make sure all keys are lowercased.

In the custom merge function, i've added k.GetString("env") to get the environment variable so that I can have diff log level on the merge outcome.
This has caused the library to hit ko.mu.RLock() and stuck.

Technically I can just remove this, but would be bad in case anything goes wrong.
Any suggestion please?
Or is there any built in way to make all keys lowercased?

To Reproduce
Use custom merge function and try to read and value from k eg: k.String("") in it.

Expected behavior
A clear and concise description of what you expected to happen.
Before introduction of mutex locks it was okay.

Please provide the following information):

• OS: oxs
• Koanf Version v2.3.0

Additional context

• The "ENV" is always available and loaded first from environment.

[BananZG]

should i just use os.Getenv("XXX_ENV") for this
(i have prefix in env provider)

[knadh]

Sorry, I missed this. Could you please share your custom merge function to see how exactly it's triggering a mutex-block?