I saw your thread before, but forgot to mention it.
I tried your suggestion and various other distributions without success.
But thank you for your help anyway, I appreciate it!!
I just found a solution to my problem though:
I destroyed the app on fly.io and re-deployed it as-is on a new instance, problem gone.
Everything else stayed the same, apart from adding these to my Dockerfile
(new lines prefixed with a +):
FROM node:18-alpine
+ LABEL fly_launch_runtime="nodejs"
WORKDIR /app
COPY package.json yarn.lock ./
RUN yarn install --frozen-lockfile
COPY . .
RUN yarn prisma migrate deploy
RUN yarn prisma generate
RUN yarn vite build
+ ENV NODE_ENV production
CMD [ "yarn", "start" ]
The only other difference I can think of, is that the previous instance was initially using a buildpack, then was changed to use a Dockerfile. Maybe that affected the instance in some permanent way.
In any case, what I did was basically to “to turn it off and on again”. It worked, I just wish I had thought of that earlier.