Etherpad plugin development: Document update conflict on using db.findKeys() - couchdb

Question

I am currently developing an Etherpad Lite plug-in, using Etherpad Lite (1.8.14) and a CouchDB (3.2.2) database. I have first written a small test function which I connected to the server-side hook 'expressCreateServer'.
const db = require('ep_etherpad-lite/node/db/DB');
function expressCreateServer(hook, args, cb) {
args.app.get(`/test`,
async (req, res) => {
await db.init();
const keys = await db.findKeys(`pad:*:revs:*`, null);
res.json(keys);
}
);
return cb;
}
exports.expressCreateServer = expressCreateServer;
I can use db.get() or db.set() without any problems, but Etherpad terminates when I use db.findKeys() and throws the following error.
[2022-08-31 08:41:43.480] [ERROR] server - Error: Error: Document update conflict.
at handleError (/opt/etherpad-lite/src/node_modules/ueberdb2/databases/couch_db.js:26:17)
at /opt/etherpad-lite/src/node_modules/ueberdb2/databases/couch_db.js:127:9
at Request._callback (/opt/etherpad-lite/src/node_modules/nano/lib/nano.js:174:9)
at Request.self.callback (/opt/etherpad-lite/src/node_modules/request/request.js:185:22)
at Request.emit (events.js:375:28)
at Request.emit (domain.js:470:12)
at Request.<anonymous> (/opt/etherpad-lite/src/node_modules/request/request.js:1154:10)
at Request.emit (events.js:375:28)
at Request.emit (domain.js:470:12)
at IncomingMessage.<anonymous> (/opt/etherpad-lite/src/node_modules/request/request.js:1076:12)
This error always occurs exactly once when Etherpad and the CouchDB are used for the first time.
Does anyone have any idea what the problem is?