I have sold three properties from my rental property portfolio this year. Why is one of the three showing as a Section 1250 property, while the others are 1245 properties from an unrecaptured depreciation perspective.

It depends on the type of rental property you sold. Section 1245 assets are depreciable personal property (furniture, equipment, etc.)  or amortizable Section 197 intangibles; Section 1250 assets are real property, whether depreciable or not. Either one of these provisions may result in capital gains and/or ordinary income (including depreciation recapture).

Also note that Section 1250 applies to assets that are not and have never been Section 1245 property. If you converted a rental from personal use, this would cause the sale to be subject to Section 1245.