Indexes are getting dropped when upgrading CBS from 6.5 to 7.0.0 with storage mode as MOI

When upgrading from 6.5.1-6299 to 7.0.0-4732, indexes are getting dropped with storage mode as MOI.

Steps to Reproduce-

1. Setup 4 node cluster KV - KV - Index - N1QL with storage mode as MOI
2. Create a bucket (standard_bucket0) and load some data
3. Create 1 primary index and 1 secondary index.
4. Stop all CBS and upgrade them offline.
5. After upgrade check the indexes in index workbench. After coming to "Warm-up" stage indexes disappears.