Seen in 2.3.15 OpenTx X9Dplus. (is also present in 2.2.4 no other vers checked)
f/w vers 2.3.15-otx(1004ef7).

When a channel has a delay or slow movement selected and is not at zero (0%, 1500us) ie, throttle at lowest value (-100%, 1000us).... when switched via a mode change, from a mode that has set a preset min value (-100% or 1000us) to a mode where that channel is at/near min value, ie throttle stick at minimum, the output value jumps to zero and changes to the minimum value set by the stick, delayed or slowed as per the delay/slow setting for that channel.
Seen on both throttle and flap channels of a F5J glider when a delay or slow movement is set as mode is switched, even though that channel is set to min in both modes. In the case of the throttle, causes the electric motor to unexpectedly start and run for the delay period, so could be a hazard.