With 5.4, this is just going to be a standard thing you need to tweak to make it work your combination of level/scene/map and your hardware when you’re using RVTs. I did a whole bunch of experiments with this over the past few days across multiple maps to make sure this is consistent.
The idea of the Transient Pool seems to be to continuously update the necessary pool size to facilitate the view you’re aiming for including all of the VTs.
It’s important to note that the message you get while moving the camera is telling you to use a Fixed Pool.
So, here’s an approach that should work in general.
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In your Project Settings, filter on “pool” and find the Transient Pools section shown in the screenshot
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Delete this pool! There’s a Bin icon on the row that says “Transient Pools 1 Array Element”. Don’t worry, the Editor is going to rebuild this for you. Keep the Project Settings tab open, you’re coming back here a few times.
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What you’re going to do now is allow a new pool to be built with a first attempt at finding your peak* requirement. Go to your Map, go high enough up to see however much of your map you normally do while working, and spin your camera round and round, fast - really! The aim here is to force the Editor to pool as much as it needs to quickly.
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Go back to your project settings and check out that same Transient Pool section. You’ll see the Transient Pool has been recreated. You’ll want to find the row that says “Size in Megabyte” - this is the dynamic size your pool is updating to try to load everything you want to see. Make a note of that number.
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At this point, I’d personally delete the Transient Pool again and repeat the spinning camera thing a few times, each time noting down the resultant number until you find a maximum number. You don’t actually need to delete the Transient Pool - the number will just keep updating as required, but I found it easier to capture the maximum this way.
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Let’s move on. It’s time to make a fixed pool. You’re going to click on the Fixed Pools “+” symbol to add a new Fixed Pool. You’re going to need to match whatever Formats you had in the Transient Pool Formats section, and then enter the Size in Megabyte that you captured in steps 4 and/or 5 as your peak requirement. You’ll end up with a Fixed Pool setup something like mine below. Remember this is going to be specific to your map and machine, so while I have a couple of DXT5 Format entries and a pool size of 512MB, your requirements may differ.
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Now it’s just a matter of repeating this - delete the Transient Pool, go back to your map, and start spinning that camera again. If the message pops up, your new Fixed Pool isn’t large enough, so go back, up the number in Size in Megabytes, and delete the Transient Pool. I’ve found it takes me 3 or 4 cycles of this to get the number right, but 512MB works well. Sure, I’m locking in half a gigabyte of VRAM for the textures when maybe a couple of hundred MB would do, but that’s a cost I’m willing to pay - I can see through perfmon my VRAM usage go up by 300MB (when I up the pool from 200 to 500) so this is a direct, measurable cost. You will want to tune for your own setup.
That’s it. The Transient Pool is going to get recreated sometimes - do something crazy to your scene, add a bunch of new textures, painting on your landscape and darting around the map - overall though, the message is going to be eliminated and you can be confident you’re not going to push your machine beyond what it can do because you spent time tuning it.
It sure is easier to just untick “Pool Auto Grow in Editor”, so if you’re doing a quick job then that’s your best solution. However, for a Map you’re actually spending time on, this is just going to force a queue to build on your in-Editor textures, so your screen is going to update a lor more slowly when you move your camera around. Like everything in UE, it’s up to you to choose the best option for your specific needs 