Hi Salmonpuff, I had to change my vial over Christmas as was having the same problem. After about 10 u of humalog I was still 17.8 - ridiculous. After 2 days of messing about I chucked the vial away and started a new one - much better! I reckon that the whole house has been warmer as we've been in more and even the kitchen has been super warm with the cooking - hence the insulin packed up.
But like you I am also on Lantus and find a massive difference even with an adjustment of 1 unit. It's a pain in the rear isn't it? Good luck with your appt. Let us all know how you get on, and if you do change insulin I'd be interested to know if it works.
All the best, Karen.