Device support suddenly disappeared - no QR code

For the past couple months I’ve been developing successfully with Expo and have had no problems loading to my Android phone using the automatically generated QR code. Yesterday I updated to the latest version of Expo, 3.27.4. Today no QR code is generated, and when I generate a link and try to open it, I get the error message ‘uncaught error: Failed to connect to /’. The phone and my computer are connected to the same Wifi router. When I try to change to Tunnel, it says 'Error starting tunnel No packager found for project at [my project directory].

Here is my diagnostic info:

Expo CLI 3.27.4 environment info:
OS: macOS Mojave 10.14.6
Shell: 3.2.57 - /bin/bash
Node: 14.9.0 - /usr/local/bin/node
Yarn: 1.22.5 - /usr/local/bin/yarn
npm: 6.14.8 - /usr/local/bin/npm
Watchman: 4.9.0 - /usr/local/bin/watchman
Platforms: iOS 13.2, DriverKit 19.0, macOS 10.15, tvOS 13.2, watchOS 6.1
Android Studio: 4.0 AI-193.6911.18.40.6626763
Xcode: 11.3.1/11C505 - /usr/bin/xcodebuild
expo: ~38.0.8 => 38.0.10
react: ~16.11.0 => 16.11.0
react-dom: ~16.11.0 => 16.11.0
react-native-web: ~0.11.7 => 0.11.7
expo-cli: 3.27.4
Expo Workflow: managed

Following up: I’ve realised that it is only this project that presents this problem. My other Expo projects launch from the Expo CLI with the usual QR code.