Do you still found the issue?
Basically, API can just provide data to the application layer as is. I would suggest you contact the data support team to check the data sent by Elektron Real-Time data feed. If the data feed does not send update data before the time you subscribe to the items, there is no way for API to generate it as well.
I would suggest you submit a data support case to data support via my refinitiv and provide item name with a time stamp or application log to the team.