To reproduce
Type in
/particle crit ~ ~ ~Add a space
Hit
escLook at the command syntax help:
[<delta>] <speed> <count> [force|normal]
The displayed syntax suggests that the <delta> argument can be left out while still specifying <speed> <count> [force|normal].
Attached screenshot shows similar situation with /particle's 18w02a syntax.
I use /particle name (for example /particle block diamond_block)without and furthur arguments, and the command works fine.