Thanks @jyotish. Following the above steps, the zip file submission now works.
Something I noticed from downloading my Colab submission was that there seems to be a reversal between claims and prices at the end of the predict.R file:
claims = predict_premium(trained_model, Xraw)
Not sure if this would have been a problem I introduced or if it related to the template linked to the submit.sh utility.
On another note, leaderboard seems to be based on my worst submission (id 110383) instead of the best or most recent ( 110384, 110389)