Slow render and dropped frames when using Fusion clips

I wanted to try Resolve for a small personal project. It was a 15-second project that included two *.dpx sequences on the timeline with a Fusion Text+ clip on top of one of them. Additionally, I had a Fusion clip with multiple *.dpx sequences in it.

Usually, because I don't have a very fast storage, I can't use maximum render speed when exporting from Resolve. However, 50 or 75 usually works fine.

But on that project, when Resolve was exporting the Fusion clips, it couldn't work well with 50 or even 25 render speed. The speed kept dropping to 0 and, when it finally finished, it had lots of dropped frames (i.e. black frames in the export).

I had to drop the render speed to 1 for it to render properly, but that meant a 15-second clip took about 6 minutes to render.

Initially, I thought maybe the problem is that I am rendering a comp that has multiple *.dpx sequences being read and written on a relatively slow storage. Then I decided to move the comp to standalone Fusion for comparison, and everything worked really well there. It finished exporting really fast (within a minute).

So, am I doing something wrong with my workflow in Resolve, or is this just Resolve 15 still being in beta?