Stiction (combination of the words static and friction) is a fuel injector problem caused by a delayed response in the injector spool valve due to static friction being stronger than the magnetic force of the injector coils which activate the injector spool valve (which allows oil into the injector to fire it). Stiction causes a common cold start issue displayed as missing, bucking, smoking when first started. Because a thicker engine oil will amplify the problem, cold starts are when the stiction problem is most noticeable. Once the engine oil warms, and thins, the stiction symptoms typically go away.
Stiction can be a problem with WVO systems that are not switched back to pure diesel early enough before shut-down to fully purge the WVO from fuel pump, pressure lines, and injectors. The thicker WVO causes sicky injector problems.