The bug

Gray italic command usage notifications in chat, which are sent when another player or a command block executes a command, can have white non-italic inserted parts when the the command was used by a player or by command block tracking the output. This is similar to MC-91499 and apparently caused by the same text-component object being used for the gray italic chat output and the white non-italic command block output, therefore overwriting the previously set style.

How to reproduce

1. Enable commandBlockOutput

   /gamerule commandBlockOutput true
   

2. Place an impulse command block, tracking the output with the following command

   /effect @p minecraft:absorption
   

3. Active the command block