fenix 5x plus running cadence has been dropping steps lately (underreporting cadence) - any ideas?

What does it look like on Garmin Connect? Strava does things that GC does not and should not be used to identify possible problems.

the cadence looks pretty much the same on GC -- you can see the cadence get cut in off regularly (the red plots). See below.

I get a very different result when using a strap to using the watch without. Without the chest strap (with running dynamics) my cadence is pretty much consistently recorded. Without,it's a bit more broken and disjointed. I can only assume then that since the accelerometers are in the watch then that is why it happens.

The troubling thing for me is that the watch itself (without any external sensors) used to record cadence perfectly, with no dropped steps, even in runs up to half marathon distance. no problems during speed workouts either.

I've been using this watch for around 6 months, and I've only recently (in the past 2 weeks) started seeing the cadence missing so badly. I am wondering if the sensor could be malfunctioning and what might cause something like this.

If in doubt contact Garmin Support.