Turns out it's probably Chromium crashing, as determined from running the command line (obtained from ps(1)
after clicking to generate an image) and running it by hand:
-bash-4.2$ /var/lib/grafana/plugins/grafana-image-renderer/chrome-linux/chrome --disable-background-networking --enable-features=NetworkService,NetworkServiceInProcess --disable-background-timer-throttling --disable-backgrounding-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-background-pages --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-features=TranslateUI,BlinkGenPropertyTrees --disable-hang-monitor --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-backgrounding --disable-sync --force-color-profile=srgb --metrics-recording-only --no-first-run --enable-automation --password-store=basic --use-mock-keychain --headless --hide-scrollbars --mute-audio about:blank --no-sandbox --remote-debu