I hove 2 Sims from different network providers in my note 9.
Sim1 for internet only(4g/3g auto)
Sim2 for calling (2g only)
Whatsapp not take chat backup auto / manual. Whatsapp showed that your internet is in roaming (while its not in roaming). while I am in my location & all other apps working good like Samsung cloud bakcup, gmail, youtube, twitter, facebook etc.
If I remove the sim2, Whatsapp took backup without any error or warning.
Kindly update if someone has idea about this , is this a Whatsapp issue or note settings etc.