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One example of latchup is if one leaves Nwell floating.
Another example is if one has a small number of substrate or Nwell contacts, a fast switching large transistor can change local substrate of Nwell potential by capacitive coupling. That can trigger latchup in proper curcumstances.
Both scenerious can happen with perfectly clean supplies.
If circuit is slow, all supplies are ideal and Nwell and Pwell are connected to supply and gnd rails, then no latchup is possible.
BUT, is power-up and power-down of your circuit slow enough?
Can nearby digital circuit inject minority carriers into the common substrate that diffuse to your slow op-amp and fire latchup then?
Is input of your op-amp is clean of high-frequency components? Can output be overdriven?
All these reasons can lead to the latchup, albeit much less probable for a slow circuit.