The easiest way is to plan ahead and make sure all your media matches up with your output displays to avoid scaling completely. If your display is 1920x1080 with a refresh rate of 30hz, you'll want a camera that captures 1080p @ 30fps, video content that's 1080p @ 30fps, and still images that are 1080p.
Failing that, Isadora scales your content to fit onto your Stage automatically (but scaling means processing power, which is why you want to avoid scaling wherever possible and just make sure that you create or capture media that fits your Stage/Display resolution and refresh rate.
There are some settings in Isadora > Isadora Preferences > Video > Video Image Processing, but generally it's best to just leave this as "Scale to Smallest"
You can use the Scaler actor to manually scale things, but again, it's better to just make sure your media and live feeds are the right resolution from the beginning.
In Stage Setup, under Display Settings, you can set custom resolutions for displays, but yet again, it's better to just leave this at the default so it matches the display (which ideally also matches the media). If the media is too small, it will be automatically scaled up to the size of the Stage to which it's being output. It it's too large, it'll be scaled down to the size of the Stage to which it's being output.
A number of systems (youtube included) simple give you a predefined selection of thumbnails to pic from. So perhaps a default of position 0% as it is, but with the option of changing a thumbnail to use 10% 25% 50% or 75% as alternative thumbnails.
Fusion can export Hap (as Fred said not Resolve), however, if you are including audio its a pain (audio needs to be linked in a separate file). I am now using 'Shutter Encoder' for my Hap mov batching. (PS Hap MOV works as well as AVI in Isadora 3) For Hap AVI, I am using Vegas Movie Studio (still my go to video editor when I want to do things fast) it has AVI render support (no batching). (needs to be the Movie Studio platinum or Suite) Losing Adobe Media Encoder is really the hardest part of dropping Adobe for me.
Affinity Photo is pretty great. I have been working on lrg print images with ~100 layers (lots of groups/folders) that are over 2gb (photoshop large file format) and they are working perfectly. Affinity Designer is also pretty nice. But I am still learning both.
Did you submit a support ticket for this issue? We'd love to help you try to solve it.
Also, having looked up this error in our system, your error might be caused by overuse of the Preload Scene and/Picture Preload actors. Try removing any Preload Scene and Picture Preload actors from your project and see if that makes a difference.
Thanks for the reply. It looks like I have solved it.
It seems the problem was indeed an over-abundance of Pre-load Scene actors that I had not found my first few looks through. I've never had this sort of "build up" problem before but it may have something to do with the fact that I was using the JumpByName actor to trigger my cues. Also, to answer your question they were movies.