Are there any consequences to mashing out at higher than normal temperatures?

Not recommended

As Molot stated your "mash" must be much lower or enzymes will denature. After saccarification, temps can be raised for protein rests mash-out etc.

Mash-out shouldn't exceed 168° unless the sparge water is treated to be below pH 6.0. If the sparge water is too alkaline (pH 6.0+) AND 170°F tannins will extract from the husks making the beer astringent.

The higher mash-out temperature shouldn't affect anything. Did you double check your process when you sparge? Are your OG numbers correct? If they're low, perhaps, you're not getting effective rinsing of your grains but are instead essentially channeling sparge water into your boil kettle. If your OG numbers are still correct with the new method, and you've changed no other procedure I'd invest in a pH meter.

At about 80 C enzymes start to denature, and no longer work. You end up with little fermentables and a lot of starch.

A rough rule is:

• 62°C for maximum fermentable sugars, mostly maltose (alcohol in finished beer)
• 72°C for maximum not fermentable sugars (body and residual sweetness)
• 82°C for mash out, and to stop any conversion

If you mash at, say, 65°C, and you only sparge at 82°C and it's bad, but was OK when you did sparge at 78°C, it means you should simply mash longer. Your previous process didn't break all enzymes before sparge, so starch could also be converted during sparge, filtration, and before boil. Now it cannot, so you need to make sure it's all converted before sparge. Consider iodine test, or two hours mash, with generous stir every 20 minutes.