to answer directly your concern - the only operation i'm aware of to run after snapmirror break is a deswizzling scan, and it can be quite impacting if the deswizzling could have not run after each snapmirror https://kb.netapp.com/app/answers/answer_view/a_id/1003882
having said that - this to actually impact just day to day office access sound maybe a bit odd. i can give some idea's to try and follow:
are the two systems the same spec? have the same network design?
what level of object do you see the latency in ? (Volume/Lif usually shows client related latency - aggregate is usually down to the local system)
are the client have the same connectivity ? (WAN connection with latency can be very impacting for day to day use like office files)
Are the clients negotiating the same protocols? (SMB version and kerberos vs NTLM - lack of SPN can cause issues.)
i think that after isolating common causes. the right thing to have is a few wireshark samples from each scenario