Are there any UPS applications that increase stress on UPS electronics?

Yes. UPSs operating with constant heavy loads, or those that support frequent load fluctuations (large motors, HVAC, medical imaging equipment) can place the UPS electronics under more stress and accelerate the wear of the internal components. UPSs that endure frequent battery discharges add stress, too. And of course, heat is the enemy of any electrical device, so high ambient temperatures can increase the risk of early failure.