Azure function apps logs not showing
The log window is a bit fragile and doesn't always show the logs. However, logs are also written to the log files.
You can access these logs from the Kudu console: https://[your-function-app].scm.azurewebsites.net/
From the menu, select Debug console > CMD
On the list of files, go into LogFiles > Application > Functions > Function > [Name of your function]
There you will see a list of log files.
Azure Portal was updated last week and they moved logs from Monitor to the home of the actual Azure Function. However, to see them you need to click Test. I raised an issue with Microsoft support and they spent several days twiddling their thumbs before I came across the answer myself. I hope this saves others a bit of time
Log messages should show under the function code, if you're watching that window at the time of the function's execution:
To view log messages made while you weren't looking, you'll need Application Insights configured. If that's configured, that should show under the Monitor tab: