Power only updated every 15 seconds during ramp intervals

Zwift ramp intervals such as the ones below are broken.

        <Ramp Duration="30" PowerLow="0.8" PowerHigh="1.05">
            <textevent timeoffset="0" message="All right, ramp it up!  Cadence ~100 RPM here."/>
        <SteadyState Duration="30" Power="1.05" Cadence="100">
            <textevent timeoffset="0" message="Good work, now keep the effort constant, cadence still at 100 RPM."/>
        <Ramp Duration="30" PowerLow="1.05" PowerHigh="0.8">
            <textevent timeoffset="0" message="Ramping back down now. Keep the cadence up!"/>

Unfortunately, the power sent to the trainer only updates every 15 seconds, so the effect is not a ramp, but simply 2 steps. Can be seen in my Zwift logs here, showing only the ERG setting lines:

[18:52:45] [FTMS] ERG 250w --> 285w
[18:52:45] [FTMS] ERG 285w --> 290w
[18:53:00] [FTMS] ERG 290w --> 325w
[18:53:45] [FTMS] ERG 325w --> 285w
[18:54:00] [FTMS] ERG 285w --> 250w

This severely changes the experience from the intended workout. E.g. in this case I had to hold 325 for 45 seconds, instead of holding for 30 seconds and then ramping down.

Experienced in this event: Escalation - The at Home Cycling & Running Virtual Training App

I remember a similar issue in one or more of the “FTP Builder” workouts.