Unfortunately I didn't have progress=plain so it's a little garbled, but this was during a fairly parallelised build:
=> [php-with-codebase 7/7] COPY --link --from=composer-output vendor vendor 3.0s
panic: send on closed channel 3.0s
=> => merging 3.0s
=> CACHED [pax-lookup-api composer-installer 3/3] RUN --mount=type=cache,target=/root/.composer --mount=source=snowfall,target=./snowfall --mount=from=composer:1,source=/usr/bin/composer,target=/usr/bin/composer if [ "false" = "false" ]; then composer validate && composer install --no 0.0s
goroutine 13959 [running]:okup-api 1/8] RUN a2enmod rewrite 0.5s
=> [pax-lookup-tester pax-lookup-tester 1/5] RUN --mount=type=cache,target=/var/cache/apt,sharing=private curl -sL https://deb.nodesource.com/setup_16.x | bash - && apt install -y npm git zip 44.0s
github.com/docker/buildx/util/progress.(*Printer).Write(0x140006d01e0, 0x140005cb1a0) 0.0s
=> CACH/src/util/progress/printer.go:41 +0x3c config config 0.0s
github.com/docker/buildx/util/progress.(*prefixed).Write(0x140001524b0, 0x140005cb1a0) 0.0s
=> CACH/src/util/progress/multiwriter.go:29 +0x60 web 0.0s
github.com/docker/buildx/util/progress.FromReader({0x104be2d90, 0x140001524b0}, {0x1044348dc, 0x13}, {0x104be12a8, 0x1400073a2c0}) 0.0s
=> CACH/src/util/progress/fromreader.go:35 +0x448mposer.json composer.lock ./ 0.0s
github.com/docker/buildx/build.newDockerLoader.func1()mposer-installer /pax/vendor vendor 0.0s
=> CACH/src/build/build.go:1368 +0x294 --link --from=composer-output vendor vendor 0.0s
created by github.com/docker/buildx/build.(*waitingWriter).Write.func1l!/pax/web!g' /etc/apache2/sites-available/*.conf 0.1s
=> [pax/src/build/build.go:1402 +0x30] RUN sed -ri -e 's!/var/www/!/pax!g' /etc/apache2/apache2.conf /etc/apache2/conf-available/*.conf 0.1s
make: *** [build-images] Error 2link data/airports.php data/airports.php
Unfortunately I didn't have progress=plain so it's a little garbled, but this was during a fairly parallelised build: