Yes, it looks like it. I placed my custom fragment first in fragment list, then also set fade duration to 50 (200 is default) and it mostly resolved the issue for now. If you set fade duration to 150 and place it to the end of list (as me b4), it will still appear sometimes, if you spam two buttons for example, so I believe this is really timing and order problem or fragments.
I can't think about a good solution, I have not examined scenes and fragments source code well
I also failed to get error with Item Set Browser today, but initially I got it every time (with Perfect Pixel enabled), so I wonder if some fragments will let you consistently avoid this error as PP removes some of them.
When I tried to open the Tomes interface ingame it produced lots of error code with this error: E89AA440. The Tomes screen failed to open from the Alt menu or with F4.


/EsoUI/Ingame/DirectPurchase/DirectPurchase_Manager.lua:42: Attempt to access a private function 'QuerySkuCatalog' from insecure code. The callstack became untrusted 19 stack frame(s) from the top.
stack traceback:
/EsoUI/Ingame/DirectPurchase/DirectPurchase_Manager.lua:42: in function 'DirectPurchase_Manager:RequestCatalog'
<Locals> self = [table:1]{fireCallbackDepth = 0} </Locals>
/EsoUI/Ingame/TamrielTomes/TamrielTomesScreen_Shared.lua:763: in function 'ZO_TamrielTomesScreen_Shared:OnShowing'
<Locals> self = [table:2]{currentCurrencyAmount = 5474, initialized = T, currentTierIndex = 1, nextTimeRemainingUpdateS = 5771.8139648438, currentRewardTrackId = 1, selectedTomeIndex = 1, pendingPreviewType = 0, areKeybindsAdded = T, selectedTomeId = 1, activePreviewType = 0} </Locals>
/EsoUI/Ingame/TamrielTomes/Keyboard/TamrielTomesScreen_Keyboard.lua:317: in function 'ZO_TamrielTomesScreen_Keyboard:OnShowing'
<Locals> self = [table:2] </Locals>
/EsoUI/Libraries/Utility/BaseObject.lua:324: in function 'ZO_DeferredInitializingObject:OnStateChanged'
<Locals> self = [table:2], _ = "hidden", newState = "showing" </Locals>
/EsoUI/Libraries/Utility/BaseObject.lua:304: in function 'callback'
/EsoUI/Libraries/Utility/ZO_CallbackObject.lua:132: in function 'ZO_CallbackObjectMixin:FireCallbacks'
<Locals> self = [table:3]{restoresHUDSceneToggleUIMode = F, state = "showing", wasShownInGamepadPreferredMode = F, fireCallbackDepth = 1, restoresHUDSceneToggleGameMenu = F, name = "TamrielTomesSceneKeyboard", disallowEvaluateTransitionCompleteCount = 1, wasRequestedToShowInGamepadPreferredMode = F}, eventName = "StateChange", registry = [table:4]{}, callbackInfoIndex = 1, callbackInfo = [table:5]{4 = F}, callback = /EsoUI/Libraries/Utility/BaseObject.lua:304, deleted = F </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_Scene.lua:151: in function 'ZO_Scene:SetState'
<Locals> self = [table:3], newState = "showing", oldState = "hidden", name = "TamrielTomesSceneKeyboard" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneManager_Base.lua:213: in function 'ZO_SceneManager_Base:ShowScene'
<Locals> self = [table:6]{remoteSceneSequenceNumber = 339, hudUISceneName = "hudui", hudUISceneHidesAutomatically = T, numTopLevelShown = 0, isLoadingScreenShown = F, numRemoteTopLevelShown = 0, hudSceneName = "hud", initialized = F, fireCallbackDepth = 0, exitUIModeOnChatFocusLost = F}, scene = [table:3], sequenceNumber = 339 </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneManager_Leader.lua:309: in function 'ZO_SceneManager_Leader:ShowScene'
<Locals> self = [table:6], scene = [table:3] </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneManager_Leader.lua:392: in function 'ZO_SceneManager_Leader:OnSceneStateHidden'
<Locals> self = [table:6], scene = [table:7]{restoresHUDSceneToggleUIMode = F, state = "hidden", wasShownInGamepadPreferredMode = F, fireCallbackDepth = 0, restoresHUDSceneToggleGameMenu = F, name = "mailInbox", disallowEvaluateTransitionCompleteCount = 1, wasRequestedToShowInGamepadPreferredMode = F}, lastSceneGroup = [table:8]{state = "hidden", activeScene = 1, fireCallbackDepth = 0}, nextSceneGroup = [table:9]{state = "showing", activeScene = 1, fireCallbackDepth = 0}, currentNextScene = [table:3] </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneManager_Base.lua:287: in function 'ZO_SceneManager_Base:OnSceneStateChange'
<Locals> self = [table:6], scene = [table:7], oldState = "hiding", newState = "hidden" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneManager_Leader.lua:339: in function 'ZO_SceneManager_Leader:OnSceneStateChange'
<Locals> self = [table:6], scene = [table:7], oldState = "hiding", newState = "hidden" </Locals>
/EsoUI/Ingame/Scenes/IngameSceneManager.lua:409: in function 'ZO_IngameSceneManager:OnSceneStateChange'
<Locals> self = [table:6], scene = [table:7], oldState = "hiding", newState = "hidden" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_Scene.lua:152: in function 'ZO_Scene:SetState'
<Locals> self = [table:7], newState = "hidden", oldState = "hiding", name = "mailInbox" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_Scene.lua:284: in function 'ZO_Scene:OnTransitionComplete'
<Locals> self = [table:7], nextState = "hidden" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_Scene.lua:279: in function 'ZO_Scene:DetermineIfTransitionIsComplete'
<Locals> self = [table:7], nextState = "hidden" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_Scene.lua:201: in function 'ZO_Scene:OnSceneFragmentStateChange'
<Locals> self = [table:7], fragment = [table:10]{animationTemplate = "FadeSceneAnimation", duration = 200, allowShowHideTimeUpdates = F, state = "hidden"}, oldState = "hiding", newState = "hidden" </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneFragment.lua:147: in function 'ZO_SceneFragment:SetState'
<Locals> self = [table:10], newState = "hidden", oldState = "hiding", currentScene = [table:7] </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneFragment.lua:157: in function 'ZO_SceneFragment:OnHidden'
<Locals> self = [table:10] </Locals>
/EsoUI/Libraries/ZO_Scene/ZO_SceneFragmentTemplates.lua:75: in function '(anonymous)'
<Locals> _ = ud, completedPlaying = T </Locals>