they still reward 1000 credits, but display like the 500 credits mission.
Mission types affected:
total XP (generalist)
total XP with Javelin (operation Javelin)
not sure about support XP with Guardian
screenshot:
https://steamuserimages-a.akamaihd.net/ugc/859488431785503239/CFB5AE64B4632FADC1DAEAB7E21BDC60247A5B4C/