This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 倊 is uncertain. It combines 亻 (person) with 忩, but the role of 忩 in this character is not clearly established.
With no clear meaning, picture a person 亻 beside a confused tangle 忩, representing something obscure or hard to grasp.
For ソウ, imagine the person 亻 sighing 'sou...' in confusion at the tangled 忩 shape: 'sou' cues ソウ.