Weird performance issue when using with express js

[wdporter]

I'm running express js v4, better-sqlite3 v7. My web app is very slow. Routine select queries take about 6-7 seconds. This is with or without the WAL journal mode. BUT when I have sqlitebrowser open on the server, with the database file open in it, suddenly queries are only around 300-500 milliseconds! — which is the behaviour I want and expect. Does anyone have any idea why this might be? What might sqlite browser be doing when opening the file, that might not be done when the file is used via express/better-sqlite3 ? If I understood that, I might be able to set it up so that the delay does not occur.