Those symptoms on your plant could be due to a fungal or bacterial disease. I suggest you pick off the effect of leaves and give additional spots continue to develop that consider taking the plant outside to spray it with a fungicide. In most cases spraying is not necessary in the diseases can be prevented by avoiding wetting the plants foliage which promotes disease problems. One additional thought is that such spots can at times be caused by chemicals such as a spray used in the house that landed on the plant's leaves. Make sure and avoid overwatering since soggy soil conditions can cause root problems which are often followed by foliage problems similar to what you described. Most houseplants really suffered when water so allow the soil to dry out a bit between waterings.
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