It is the most challenging thing for small companies. Chat is here, the phone calls are right there, the user's database is over here, and the developers' tasks are in that corner. Making things beautiful and accurate so that everything is clean and clear takes time; it's cumbersome and requires investments; thus, if it "used to work for three years and it was ok," then let's work with what we have.
The task: detect the connection between the ticket, where the customer awaits a follow-up, with a ticket, where a similar issue is under investigation (fixes, sales, enhancements, discounts, and so on).
I don't think I need to explain why it is good to do this. If the connection was detected correctly, you would not forget to notify the customer, and the time of informing a specialist from another department of all the ticket details would take one minute instead of ten minutes.
There is still a hint in case of no automation: use internal notes in tickets to save the details needed for further handling + a link to the internal task assigned to the technical or marketing departments. And vice versa. A task in your tracker should contain the links to the communications with a customer so that you can always add the missing details and build a list of scheduled notifications. Once the status of the task has changed, you see which customers need to be updated.
Use API and integrations. Sometimes the treasure is right in front of you. For example, the integration of a tool you got used to creates new possibilities. Connecting customer ticket system and bug tracker, setting notifications, or automation of status changes — these things are not obvious, so do not be lazy and read updates from the software vendors, be pro-active. Intercom, for example, offers integration with Trello and Jira, but you easily can miss it when reading a long list of their offers.