Possible additional stress caused by extra expansion, possible material reduction in yield or strength, especially for cast materials, corrosion resistance,
So many possibilities that only the vendor will be aware of.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
If this pump is on VSD, there may be further constraints on min permissible speed, which may require a recirc seal fluid cooler to keep the seal cool at low speeds.