Render with Fusion Composition slow down

I have a problem that I can't solve (resolve Studio 19 on Windows, GPU 3090)
I'm editing (or rather I finished) an event, a classroom course that lasts 2 and a half hours.
Since I was asked to put lower third almost constantly, I made a fusion composition for each speaker, animated at the entrance and exit with name, title and logo, using keyframe stretching to be able to lengthen and shorten at will.
Now, when I launch the rendering, at the beginning on the shots with lower third rendering runs at 30-40 fps. As the rendering goes on, everything slows down, and on the last shots the rendering drops to 2 (!) fps.
Of course: if I stop, exit and re-enter the program and start again from those same shots, the rendering normally goes fast at 30-40 fps, to slow down later.
In this condition the rendering lasts over 8 hours for a content, in HD, of 2 and a half hours.
At the moment I found a workaround: pre-rendering the lower thirds in prores 4444 and replacing them everywhere with the fusion compositions. In this way the render lasts less than an hour.
But I wonder, why a composition that renders at 30 fps when you open the program has to drop to 2 after a while? Is there a solution? Because rendering dozens of lower thirds takes time, the compositions are much easier to use.
Moreover I think that there is a problem in the programming, because such a slowdown can only be explained by a non-optimal management of resources and/or memory.
Has anyone noticed anything similar?

Most types of lower third animations when properly optimized should run pretty smoothly, and probably kill your machine when optimized poorly as you have found out. So that is where I would be looking at. Optimization of the animation and how it is used.

If the frame rate drops over time, its almost certainly caching issue there either an optimized settings for fusion/resolve eat up all the resources you give it or the animation is not optimized so when it runs out of VRAM it slows down to a crawl.

If the problem is in the settings of resolve, check in the settings what the available memory and all that is set to. If the problem is with the animation, which often it is, than you can optimize the actual animation.

If you want to, share the lower third node and I can take a look at how to optimize it. Usually with lower thirds it would probably be DOD (Domain of definition), turning off unneeded updates for nodes and possibly reducing rendering of the composition when lower third graphics does not need to be seen on screen by rendering the animation elements. Either in fusion or in edit page.

If you have particularly demanding animation you can always cache it from resolve using for example saver node or cache to disk. If you use saver node to export .exr image sequance at DWAA, with RGBA channels you can get very small file size with transparency and good quality. Once rendered it should play back at real time speed, regardless of the complexity. But most of the time its not really an issue if you optimize it and don't have some particularly demanding animation.

Like I said, the first thing to look at which can cause issues is DOD and update of node that don't need to be updated. Especially if you are using images like logo etc.