Execute this command from chat, then from command block.

/title @p actionbar {"text":"3   non-breaking-spaces"}

or this one:

/tellraw @p {"text":"3   non-breaking-spaces"}

or any other text related JSON command even nested in execute:

/execute @p ~ ~ ~ /tellraw @p {"text":"3   non-breaking-spaces"}

Expected:

• same output:

  3   non-breaking-spaces

Actual:

• different output:
  CHAT:

  3   non-breaking-spaces

  COMMAND BLOCK:

  3non-breaking-spaces

Possible cause:

• The way text is parsed and formatted from chat is different from command blocks.

( is used to represent the 'bugged' [nbsp] character)