Loose spokes on non freewheel side factory built rear wheel
 

Entire left side spokes are loose (squeeze test) rim is Sunrims M13II ridden 6 months, is this bad news or my fault for not checking spokes more often?

It depends. Geometry forces the non-drive side to be looser than the drive side of dished wheels.

If nipples are unscrewing lubricate the sockets with oil, tighten the drive side to an appropriate uniform tension (110kgf is a start) and set the non-drive side to whatever it takes to center the wheel.

Does the wheel run true / is it centered? the non-drive side will be looser than the drive side, as long as they are all a similar tension, shouldn't be too much of an issue.

While geometry forces less tension than the drive side, non-drive spokes with insufficient tension allow the nipples to unscrew as their tension drops too low when they pass the bottom of the wheel. This can happen when the entire non-drive side (and therefore the drive-side since NDS tension is a fixed fraction of DS tension dictated by geometry) is uniformly slack or with just a few spokes that are loose (with neighbors that are too tight or bends in the rim).

Well wait a minute... How loose are they? Are they slack or are they just looser than the drive side? Because if the answer is the latter and you have a multi-speed freewheel on one side, then look up "dish" and see why the left side spokes have to be looser than the right in a dished wheel.

If they're slack, then the build was bad. Get them tensioned and stress relieved. Hopefully you don't start breaking spokes.

What we don't know is how loose the OP's spokes are, I have a wheel (Veloce on Open Pro) built about 15 years ago by a LBS, the NDS spokes are loose to the feel compared to the Drive side, but not to the point where the spokes could unscrew and the ride is great on it, now if it was too loose, and the spokes were unscrewing, that would be an issue

The latter is called maintenance , if the wheels were not tensioned and trued
upon delivery from the machine, they should have been before ridden.

Spokes so loose you can turn them by hand and rim starting rubbing brake pad (what got my attention)

This indicates that even the drive side spokes are too loose. The wheel builder didn't do his job properly.

Thank you all-since I bought the wheel from my LBS perhaps they will put it right.

We get cheap, machine built wheels that do this after a few rides from time to time......we lube the nips, bring them back up to tension and equilibrate them and add a drop of Spoke Freeze to each nipple. No more problem!

I unearthed a thread from 2005 warning that the factory built rear wheels (Sunrims M13II rim) were prone to under tensioning and it happened again I guess.

The Sun M13IIs are very soft cheap rims to begin with. Crappy joints on most...plus they seem to be the rim of choice for companies building el-cheapo 700c and 27" unfinished machine built wheels. Try working one on a coaster brake hub - watch what happens when you go 1 kgf past 95 kgf.

=8-)