And now for the sources (and explanations):

Service 7A is a new route, operated by First Essex.
https://bustimes.org/services/7a-hadleigh-hockley#map

Routes 7, 21C, and 63 have changed operators: 
- 21C and 63 from NIBSbuses to First Essex
- Certain services on the 7, formerly run by Stephensons of Essex, are now operated by First Essex. Journeys on route 7 operated by Arriva Herts & Essex are unaffected.
https://bustimes.org/services/7-southend-rayleigh
https://bustimes.org/services/21c-hadleigh-morrisons-benfleet-rail-station-seavi
https://bustimes.org/services/63-the-weir-police-lodge-via-barling-rochford

Routes 21, 26, 27, and 28 had minor changes to bus operator tags ("First in Essex" to "First Essex").
https://bustimes.org/services/21-southend-creek-road
https://bustimes.org/services/26-hadleigh-leigh-on-sea-westcliff-on-sea-travel-c
https://bustimes.org/services/27-southend-travel-centre-london-road-kents-hill-r
https://bustimes.org/services/28-southend-benfleet_pitsea-basildon