In the book Lithuania 700 Years, edited by Dr. Albertas Gerutis, page 176, under chapter The Boundaries of Lithuania:
"After World War I, the boundary between Latvia and Lithuania ran along the borders of the Kaunas and Kurland governments, as it had in Czarist times. Yet these boundaries were not always precise and did not follow ethnographic lines. On September 28, 1920, both governments signed a treaty, according to which both states formed boundary commissions. Since neither commission was able to reach an agreement, the final decision had to be made by a neutral chairman, the British observer, professor James Y. Simpson.
Even though Lithuania had to turn more territory over to Latvia than she received in return, the chief gain was the historical Lithuanian coastal center of Palanga, and the mouth of the Sventoji River."
In a map printed from The Problem of Lithuanian Boundaries, the boundry line changes often in the NE corner of Lithuania, near Daugavpils, looking like Lithuania lost some ground there.