IPA: /ˌdɪs.kənˈsɜːr.tɪŋ.li/
KK: /dɪsˈkɒn.sɜːr.tɪŋ.li/
In a way that causes confusion or worry; making someone feel uneasy or disturbed.
The sudden change in plans disconcertingly left everyone unsure of what to do next.
Disconcertingly → It is formed from "dis-" (meaning apart or away) and "concert" (from Latin "concertare", meaning to bring together or agree). The suffix "-ingly" indicates a manner of doing something. Thus, disconcertingly means in a manner that causes confusion or disrupts agreement.
Think of 'dis-' meaning apart and 'concert' meaning to bring together — disconcertingly describes something that causes a disruption or confusion in agreement.