Designer High CPU/Not Responding when opening views

Hi All,
We’ve just today developed an issue that is preventing development on complex Perspective views.
Using v8.1.2, Gateway on a Win 2k19 Server & Designer on Win 10.

When opening complex/large views, it takes a long time with high CPU usage on the Designer PC before the view is opened. Designer is unresponsive during this time.
Once the view is opened, Designer is very slow.
The views have several templates, some nested, along with a few hundred tag bindings (direct, indirect & expression).

I see no errors or performance issues on the gateway, it appears to be Designer PC related and is occurring on multiple PCs.

Designer console output:

12:05:16.759 [AWT-EventQueue-0] INFO Perspective.Designer.Workspace - Launching view with DesignerPageParams 'Project', tab id 'Page/Views/Inventory', using base url http://*.*.*.*:8088/data/perspective/design
12:05:16.773 [AWT-EventQueue-0] INFO ViewResourceEditor - Perspective remote debugging port open at: http://localhost:9222/devtools/inspector.html?ws=localhost:9222/devtools/page/****
12:05:16.778 [AWT-EventQueue-0] WARN Perspective.JavaJsBridge - Bridge target 'window._designerStore' received unexpected return type 'null' 
12:07:17.252 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Views/Inventory@D
12:07:17.253 [Browser Thread: 36859] ERROR Perspective.Designer.Workspace - level: LEVEL_ERROR
message: "[mobx] Encountered an uncaught exception that was thrown by a reaction or observer component, in: \'Reaction[structure-sync]\' TypeError: Cannot read property \'getStructure\' of undefined"
line_number: 1
source: "http://*.*.*.*8088/res/perspective/js/mobx.umd.min-5.14.2.js"

12:07:17.254 [Browser Thread: 36859] ERROR Perspective.Designer.Workspace - level: LEVEL_ERROR
message: "[mobx] Encountered an uncaught exception that was thrown by a reaction or observer component, in: \'Reaction[selection-config-details]\' TypeError: Cannot read property \'findChild\' of undefined"
line_number: 1
source: "http://*.*.*.*:8088/res/perspective/js/mobx.umd.min-5.14.2.js"

12:07:17.256 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Title@D$0:0
12:07:17.262 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:1
12:07:17.265 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:2
12:07:17.268 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:3
12:07:17.271 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:4
12:07:17.274 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:5
12:07:17.276 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Page/Embedded/Inventory_Stack@D$0:2:6
12:07:17.287 [Browser Thread: 36859] INFO Perspective.Designer.Workspace - store.Page: Cannot send 'view-stop', disconnected. view=Menu/Menu@D$0:4