Having worked in finance myself, as part of a team that procured and replaced an international core banking system with a state-of-the-art, multi-hundred million dollar successor; we've never had a strong consistency requirement. Much weaker forms consistency sufficed for their needs and the requirements of regulators.
Also what big trouble do you mean? I do not know of any financial regulators that expect banks to have a totally consistent point-in-time view of their balance sheet. Furthermore the Basel Accords and similar banking supervision rules do not mandate such a requirement.
I be very much grateful if you could provide me with this information, as I can pass it to my former colleagues who will be quite surprised to discover this requirement.