Need "read more" tag fix – Does not show without featured Image

I know this is a theme vendor issue and I have had troubles with Yith themes on this issue.

They made a theme, my client bought, that requires a featured image attached to a post in order that the “read more” tag link be displayed. Without a featured image, the post excerpt does not display the “read more” tag, even when the link is manually inserted into the post.

I hope that someone can help with some PHP coding to fix this, and remove this restriction.

I already tested the site by switching to one of the WordPress default themes and the read more tag appears, without any featured image. So yes, its a theme created problem and why would a theme author even put that restriction into the theme is beyond me.

Can anyone help with PHP coding in this issue?

Thanks