Last modified field in collection is incorrect

I am using Kinto on local server by installing on system. Kinto stores a 'last modified' data field whenever we insert a document in 'Kinto' collection. I found an issue with 'last modified' field whenever I inserted the data. The 'last modified' is an unix timestamp. I tried converting the unix timestamp to the Date format, and that doesn't matches with the time when the document was inserted. What's more fascinating is -
When I insert 2 documents **consecutively**, the 'last modified' timestamp when converted from unix to date format, varies hugely. Example -
new Date(1649841497793);
Wed Apr 13 2022 14:48:17 GMT+0530 (India Standard Time)
new Date(1649861297794);
Wed Apr 13 2022 20:18:17 GMT+0530 (India Standard Time)

No file or test is named in the report. Start by reproducing two consecutive document inserts and inspect how Kinto assigns the collection's last-modified timestamp; done means the stored value matches insertion time and does not vary by hours between consecutive inserts.

Written by the indexing model from the issue text.