Pharmacists discourage crushing more than one medication at a time because of the possibility of altering the effectiveness of different medications. Healthcare workers do in fact crush a collection of meds at a time in order to process doses quicker. Caution is needed to make sure combining medications can be done without degrading or making the combinations dangerous.
As of 2/28/2022 every pharmacist surveyed from among RxCrush customers, recommends that only one medication be crushed in a dose. That may include several pills of the same medication but not a mix of different medications.
There is guidance about crushing medications and avoiding errors that can be uncomfortable for the patient and healthcare workers. This article by Matthew Grissinger, RPh, FASCP as published in P&T. 2013 Oct; 38(10): 575-576 recommends best practices for the administration of crushed medications. The article specifically recommends crushing one medication at a time. Footnotes at the end of the article point to literature with detailed descriptions of medications that shouldn't be crushed and medications that shouldn't be mixed.