In the Replication Monitor, you can see a message for a long time in the tab “Distributor to Subscriber History”.
When you see this message, in the Pending commands box on the “Undistributed Commands” tab, you can see that many Transactions have not yet been sent from Distributor to the Subscriber.
This can happen if many new records or major updates are installed on the Publisher side. Just be calm and patient. You will see that all Transactions are transferred over time.
As a precaution, you can also extend the value of the Transaction Retention Period in the Distribution Properties, whose default value is 72 hours.
Thus, you can avoid reinitialization for some subscribers. But after everything is back to normal, I recommend that you bring this value back to its default value, 72 hours.