The following effects aren't applied to the MULTI I/O section. This is part of the unit's specifications and not a malfunction.
・ SEND
・ BEAT FX
DELAY, ECHO, PING PONG, SPIRAL, REVERB, TRANS, FILTER, FLANGER, and PHASER.
However, if [MULTI I/O] is selected with the input selector switch, the unit's built-in FX will be applied.
For details, see the block diagram in the specifications section of the Instruction Manual.
You can read the Instruction Manual [here].