FN-2019-431 has been published to bring awareness to some changes made in the the SLX 9850 Management Modules. The memory in newer revisions has been increased to 32GB, from 16GB. The 32GB MM has been shipping since early 2018 but having mismatched modules is not recommended.
Please take a look at the field notice to learn more:
FN-2019-431 - SLX 9850 32GB Management Module Swap Process