It's impossible to get 100% alcohol and it's probably difficult to get 99% alcohol too. I know that they sell it as 99% Iso (I buy the stuff) but I suspect that it's a little less than 99% by the time that we use it. I doubt that it's the strength of the original alcohol that is causing the issue but it could be that polishing in a rather high humidity could be trapping moisture, coupled with the oil and it will form an emulsion. I'd try the gentle heat advice, often it will drive off the moisture.
Even a non drying oil will form a gummy deposit if (a) too much is used (b) the oil isn't removed between polishing sessions. If that happens you usually see witness lines when trying to rub it out, similar to using an oil varnish. That's why it's always important to remove as much oil as you can. You can gently mop it up with kitchen absorbent paper or even baking flour, then spirit it off in the normal way. If you use very little oil there really isn't a need to use the paper or the flour.
The highly processed shellacs (dewaxed blonde/platina) have a relatively short shelf life in the dry state. Waxy types seem to last decades. Once mixed you might get 4 months or so out of the dewaxed, bleached varieties. They slowly lose their drying/hardening ability. Again, waxy types have a shelf life a little longer, maybe 6 months or more. A lot depends on local conditions and how fresh the dry shellac was in the first place. I've never seen old shellac cause the cloudiness issue though, usually old shellac is difficult to dissolve in alcohol or it doesn't dry/harden very well.
