Thank you for the question and good photos. Your plant has an infestation of scale insects. There are many different ones but yours might be a soft scale insect. With heavy infestations, the plant will lose vigor as the insect uses its mouth parts hidden under the "shell" to suck the plant sap. With soft scale, you will also see honeydew, a sticky secretion that appears on the leaves and drips onto surrounding surfaces. You will need to remove the insects and scout the plant frequently to remove new ones that pop up. Be sure to look under the leaves.  
Read about control measures under the "Scale Insect" tab of our publication on managing houseplant pests:  https://extension.umn.edu/product-and-houseplant-pests/insects-indoor-plants
This publication from Colorado Extension goes into more detail:  https://extension.colostate.edu/docs/pubs/insect/05595.pdf

Good luck and thank you for contacting Extension.