After configuring an LDAP User Store and adding the initial connection information, the error "mcc.ui.invalid_cohort" is appearing.

The User Store Name chosen had an invalid invalid character. When creating an LDAP user store, this configures a new tenant internally, therefore invalid characters for tenants also apply to the LDAP user store name.
eg:

LDAP User Storage name: MSSN.mss

In this instance, the User Store Name chosen (MSSN.mss) had a full stop/period (.) in it, this is an invalid character.

AXA : 17.3.x

Avoid any special character for use in LDAP user store name/tenants.

Configure the LDAP User Store
https://techdocs.broadcom.com/content/broadcom/techdocs/us/en/ca-enterprise-software/it-operations-management/app-experience-analytics/17-3/administrating/set-up-the-administration-hierarchy/tenant-administrator.html#concept.dita_d1012340bdab940be3ef6f3da3b25af872dfe451_ConfiguretheLDAPUserStore