The bug

Effect commands fail if the target already has the effect but with a higher amplifier, this is as intended. The bug is that the command does not completely fail, the hideParticles option gets carried over.

How to reproduce

• Make sure you have no status effects on you.
• Type in chat:

  /effect give @s haste 1000 0 true

• As expected you now have the Haste I effect for 1000 seconds with no particles.
• Type in chat:

  /effect give @s haste 100 1

• As expected since the amplifier is now higher (1 > 0), the effect you had from the first command gets overwritten by this second command. You now have Haste II for 100 seconds with particles.
• Type in chat:

  /effect give @s haste 1000 0 true

• Since the amplifier is now lower (0 <1) than your current effect from the second command, the amplifier and time do not get overwritten, so you keep Haste II for whatever time was left of the initial 100 seconds. However, the command does not fail and the particles disappear. The "true" from this third command has overwritten the (default) "false" from the second command.
• Type in chat:

  /effect give @s haste 1000 0 true

• This is the same as the first and third command, however now the command fails as expected because it couldn't overwrite the hideParticles option again (the third command already did that).

What I expected to happen

I expected the third command to completely fail like the fourth command because the amplifier was lower than the already applied effect and not overwrite the hideParticles option.