When some but not all bullets end with a period in a PPT. Drives me nuts! Either have none ending with a period, or all need to have a period, but please don't mix.
The way I do it is if a list only has single sentences or sentence fragments, I omit the period.
If there is at least one point with two sentences, everyone gets a period.
If a list has sentence fragments and double sentences, I cry. Then I rewrite the fragments into complete sentences, complaining about it the whole time.