Maybe dynamic is a nullable field, but is not a nomal condition for other dynamics in the system.
/interface pppoe-server
add name=pppoe-in1 service=“” user=teste
NOT WORK
print where dynamic=no
NOT WORK
remove [find dynamic=no]
WORK
print where !dynamic
NOT WORK
remove [find !dynamic]
WORK
print where dynamic!=yes
WORK
remove [find dynamic!=yes]