Issue search requires JSON value on Custom Fields (Cloud)
There are some issues related to how searches filtered by MLCS custom fields are handled in both Server / Data Center and Cloud instances:
BASIC SEARCH
When using the basic search, you can choose a field and add value to it to refine the search. Unfortunately, you cannot choose the selection as intended (dropdown selection). Instead, you are required to pass a JSON value to filter by that field.
JQL SEARCH
A similar behaviour occurs when using JQL queries. A JSON value needs to be passed to make the filter work with custom fields.
The current field type only supports this type of request. While we have plans on our roadmap to develop a new field for a more seamless search experience, for now, this appears to be the most effective way to perform searches using the MLCS custom field.