"No train" or "prices unavailable"

Hi everybody,

Thank you for reading my message first and any help would be appreciated, nice day :)

Here is our problem :

Venice - Ljubjana 30/07 in the morning
"Prices unavailable from Venice to Trieste for mandatory seat reservations
Is this because seat reservations are not yet available or should we find an alternative?

Bari - Rome 12/08
"No train”

Rome - Milan 14/08
"No train”

For our other destinations, we are too early, so we will wait to book (90 or 60 days before on average).
But for the 3 routes above, is it also because we are booking too early? Because the site does not give any details

Or should we worry and think about another route?
Thanks for your help :)

Louise