Does this sound natural?
But it’s just a tentative schedule. The update might be quite sporadic.

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@fukutaka

It’s generally a good idea not to start a sentence with “But”. If you want your sentences to sound more natural and less rigid then try not to use several smaller sentences to convey a singular thought.

Your sentences are perfectly fine for conveying information and comprehension, but you can make a few small changes if you want to focus on being more natural.

This is cause/effect so you haven’t changed the subject between sentences.

A couple variations would be the following:
“The schedule is tentative due to sporadic updates.”

“The schedule is tentative because of sporadic updates.”

“Sporadic updates have resulted in a tentative schedule.”

“Due to potentially sporadic updates, the schedule will be tentative for the time being.”