D&D 5e Multiclassing Spell Slot Calculator
The problems with multiclassing warlock spell slots seem to persist through patch 1.
Artificer Multiclassing and Spell slots - forums.giantitp.com
When multiclassing, you combine the levels of your classes accordingly (see previous section) to determine how many spell slots you have of each level.
Best Baldur’s Gate 3 Multiclass Warlock Build - Deltia's Gaming
Multiclassing as a Warlock will grant two first-level spell slots that refresh on short rest, allowing you to cast spells like Grease or Magic Missile more often.