as @SidViscous has already pointed out this seems very much A (likely) unsolvable problem with ethanol extraction (keep them terps!)
louching into a hydrocarbon (pentane) helped, but didn’t really solve the problem as far as I could tell. @tweedledew wasn’t working with the greatest of terpene profiles to begin with, and I don’t recall sampling the results +/- louching, so your milage may vary.
do you have analytics on that fraction?
what percent is actually terpenes?
how much THC/THCA is in there?
I assume you’re already doing as @tweedledew suggests, and separating your fraction before decarb…but you’ve got 30-40% THCA in with your terps.
even if they don’t, part of the problem is that many mono-terpenes have boiling points lower than or very similar to ethanol. So simple evaporation/distillation isn’t going to get the job done.
best I’ve got would be louche into (say) pentane then try various magic dirts/solvent systems to achieve separation between your terps and your cannabinoids. the ethanol will be gone and you might have a terp fraction than no longer requires decarb. rumor has it this separation can done using lighter hydrocarbons. see Color remediation chromatography for details.
I don’t claim to be a chemist, so blame @MagisterChemist if it doesn’t work 
this is not quite the same strategy @SidViscous is suggesting, but seems at least as convoluted.
@NoHeatNoVacuum seems to have the simplest and most effective solution: No Heat No Vaccum
@SaigoMachuPicchu: that is THCA crystalizing.
Your decarb step is insufficient.
I recommend Decarb under pressure to retain terps? which is also explored under So I made a thing to decarb with