Mealy bugs or scale probably. Check the top and bottom of the leaves this time of the year with some regularity. They suck the sap off the leaves and prefer new foliage but can be found anywhere within the plant's leaves. They can eventually kill some plants so act on it now. Put some rubbing alcohol in a cotton swab and get these pests very wet with it. Try not to get alcohol on leaves as some leaves may not like that. Dead bugs may turn brownish. Check all leaves, both sides of leaves, stems and the base of the plant and the top soil. In severe infestations, maybe consider "quarantining" the affected plants so these guys will not easily jump to healthy plants. You can also try to use some chemicals but it is probably too hot to use neem oil now and these guys cover themselves in a protective cottonish wax.
