Apple has just released macOS Mojave 10.14.5 Supplemental Update for certain MacBook Pro models. To tell if your Mac requires this firmware update, use the Software Update pane. It should also be listed as an available update in LockRattler.
The models which Apple says are likely to need this update are MacBook Pro 15-inch with T2 chips, which should be 2018, identifiers MBP15,1 and 15,3.
A standalone updater is available from here.