Transaction (Process ID XX) was deadlocked on lock resources with another process and has been chosen as the deadlock victim

You may get deadlock exception when running a substitution rule. 

This could be because you have more than one rule in a rule block running against the same table. More about ensuring you set up appropriate dependencies to avoid deadlocks can be found here: https://www.red-gate.com/hub/university/sql-provision/masking-rules-and-concepts/rule-blocks-dependencies

And more on speeding up substitution rules and improving concurrency can be found here: https://www.red-gate.com/hub/university/sql-provision/performance-enhancement-with-data-masker/