Wrist pain

Garmin advise that the watch is NOT worn over your wrist bone as it can;t give correct readings for heart rate there. (It's here somewhere in the forum but I can't find the link to it).

Try wearing the watch above your wrist bone where it is more normal to wear a watch.

But unfortunately, this is not going to stop the watch from sliding into the wristbone as you run and giving you an owie.

See also https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-5-series/128545/wrist-pain-while-running

I have the same issue. I've partially solved it by getting a silicone case for the watch. Still bangs, but impact not so painful.

Other ideas/tips

Slip the watch around to the inside of your wrist. HB sensor still works. I do this especially when running around near boulders as it protects the watchface as well as by wristbone

Consider some other thing on your arm between the watch and the bone as a protection? (I've used a doubled buff /head-toob occasionally to good effect during ultras)

Make sure the strap is done up as tight as you can, without it being uncomfortable. (This helps with hb sensor too)

Don't expect to be able to wear the watch 24/7 (I get away with 8/7. Can't stand wearing it at night...)

Sweaty skin during a run makes it worse. Possibly a different watchband other than the rubbery one might help.

It's not a problem with the watch but rather your hand. A sports watch should be worn above your wristbone and tightened enough to not slip, but not too much to not cause irritation. 

The problem is that some people just won't get a good fit. All you can do is try an aftermarket band. Garmin bands are some of the most comfortable on the market though, so you gotta try looking for something that has a completely different type of adjusting mechanism. 

I got red rashes easely, I wear my fenix5X on the left and on the right wrist. At work (hospital) I wear my Fenix at the ancle. I wash my Fenix almost dayly with mild soap and water and dry it. This works better for me than just left wrist and it seems to give quite good steeps and HR.

I had the same problem with stock strap band, try a new silicone band (Amazon). Much more flexible allows to tighten the watch and avoid balancing while running.

I think the problem is that the total watch weight is not compensated: very light and thin strap vs "heavy" body (metal).

Thanks all, yes I was not wearing it over my bone! Not sure that is possible. I will try a different strap, alternate hands is also giving some relief.

I've been experiencing numbness, and swapped hands.. Noted the numbness transfered to the other, so stopped wearing my fenix5 altogether.. 

Yes! I just started wearing my watch Garmin vivomove full time for week during the day only taking it off at night while sleeping. Last night I woke up with the most excruciating sharp burning pain shooting down my wrist to my fingers and up my arm. The area where the pain was comming from was directly where the watch face sits. It lasted several hours. I wear the watch loosely on my wrist so it was not caused by pressure. In the morning the pain had subsided and I put my watch back on but towards the afternoon the pain started to faintly return so I took my watch off and now I am so scared to use it.