@Neha33 You may have to raise a Support ticket so we can look further into this but we have recently come across a case where the segmentation for lookup attributes from a relationship was not working due to a missing schema relationship descriptor:
"xdm:descriptorReferenceIdentity"
In the above case, deleting the lookup relationship from the schema and re-creating it straight away re-generated the descriptor and segmentation re-started as expected.
I have no further details on what may have happened (schema creation, further unknown actions, timings.. etc) but I thought I'd mention this. If this does not help, as I said please raise a Support ticket.
Also see https://developer.adobe.com/experience-platform-apis/references/schema-registry/#operation/listDescr... to list the current descriptors