I had a similar problem with two new mags for my Smith 539. Was looking for a mag loader assist, but managed to get all rounds loaded. Once I let them sit for a few weeks loaded, they seemed to soften up and now loading is stiff, but very manageable.
After hearing some of the experiences here with the Sig 365, I'm leaning very strongly to getting one to replace the 539 as my carry firearm, Maybe a Christmas present to myself.
Here in Reno we have gone over 30 days without any rainfall, and it looks the same for the next 10 days. Humidity is sitting at around 15% and temps in the low to mid 90's, I?m just holding my breath on the start of a mess of wildfires. So far so good!