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Scale will attack any plant, but they are more attracted to plants that are weakened. I would check the plant to see if it might be under stress from something (under-watering, lack of nutrients, etc.) and correct this while also treating the scale infestation.

It is likely the cold caused the damage, as it would affect the tree in this way (the closer to the ground, the more ground heat would have kept the frost off). But just to be on the safe side, I would treat the tree with neem oil. This will treat the tree for both any possible fungus or pests that may be attacking the tree.

If you prune just after flowering, you should be able to get more flowers the next year. This article has more information: https://www.gardeningknowhow.com/ornamental/shrubs/pittosporum/growing-japanese-pittosporum.htm

Japanese Pittosporum grows well in the shade.

For more information about Japanese Pittosporum, please visit the following link:

https://www.gardeningknowhow.com/ornamental/shrubs/pittosporum/growing-japanese-pittosporum.htm

Pittosporums generally do well with heavy pruning. The combined heat and pruning may have stressed the plant. A stressed plant can become vulnerable to insects or disease. Look for any signs of other issues on the plant and treat if you need to. Neem Oil is a good treatment.
I would wait and see.
Here are a few links for you.

https://www.gardeningknowhow.com/ornamental/shrubs/pittosporum/growing-japanese-pittosporum.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

How is the soil (i.e. drainage, moisture level, etc.)? Have you watered frequently or had a lot of rain? Pittosporum are well known for having issues with root rots, most commonly attributed to Phytophthora. Here is more information: https://www.gardeningknowhow.com/plant-problems/disease/what-is-phytophthora.htm