Hi,
Please check and follow below steps.
1. Lock your source system
2. Load all delta records to bw side and keep all queues(SMQ1/SM!3/LBWQ and RSA7) 0 reocrds
3. Once source was upgraded, Test all the loads working correct or not.
4. if any failures at data source level, then you may need to replicate the data source and activate it.
its depend on the error.
5. Actually due to the source upgrade, some time data source/extract structure will go inactive. need to check on it.
Thanks