Scale insects.

Likely they were on the plant when you brought it indoors.

scale is impervious to topical solutions ...

you either pick them off... smother them with oil ... or treat with a systemic ...

all my houseplants go outdoors for summer.. in early fall.. i treat all the media with a systemic.. outdoors.. and then bring them indoors a week or so later ....

if you want to go the oil way ... timing is imperative.. to insure you attach the CRAWLERS ... this years hatch .... as they have no hard shell at that point in the life cycle ...

but for me.. finding that 3 day window of opportunity remains a mystery.. as life usually got in the way.. during those few days ...lol.. which is a very fancy way of saying i forgot... lol ..

ken

ps: i doubt.. your insecticidal soap was labeled for scale.. so that would have been your first clue of the failure of that method ... BUT!!! ... also note.. a dead one.. looks like a live one.. so scratch a few off.. look underneath ....and determine if you actually have a current problem ... suck it up.. they dont bite ... [they suck.. lol]

You DO NOT have to treat scale in the crawler stage if you are using oils. It is effective in all the insect's stages from egg to adult. It is contact poisons where you need to get the treatment done in the crawler stage.

Insecticidal Soaps are not the usual control for scale on plants, horticultural oils are however. With a house plant you probably should not spray a dormant oil, even though that tree may not be actively growing, but a superior oil could be used.
The linked article may be of some help, although the suggestions about predators of scale may not be of much use on a house plant.

Here is a link that might be useful: control of plant scale

It is contact poisons where you need to get the treatment done in the crawler stage.

==>>> yes.. and they used a contact treatment called insecticidal soap ...

hence my comments about when that MIGHT have worked ...

obscure as my wording might have been ...

the easy solution.. is to get a systemic soil product LABELED FOR SCALE .. drench or granule ... and find a two or 3 day forecast.. where you can do it outdoors so it wont stink up the house ... and be done with the problem for years to come ...

and if its not a major population.. suck it up.. and scrap them off with your fingernail ... yeah.. i know.. yuck.. lol ...

there is no hurry .... they will nearly have to cover the entire plant .. before they kill it... so wait for good weather.. if you like that suggestion ....

ken