Observe the log to see the following warning reported about invalid params for "doc_pos" and then "page_size". Really, I think the issue is that they're missing mandatory parameters rather than being invalid. An invalid parameter to me would suggest using a parameter that isn't defined within the C++ codebase or a param that has been typo'd. Another option is instead of dumping a warning for missing mandatory params, just assume (without warning) a default if not user-defined in XML?
2024-03-08T14:46:16Z WARNING # llcommon/llinitparam.cpp(217) LLInitParam::BaseBlock::validateBlock : Invalid param "doc_pos"
2024-03-08T14:46:16Z WARNING # llui/lluictrlfactory.h(217) LLUICtrlFactory::createWidgetImpl : D:\Program Files\SecondLifeViewer\skins\default\xui\en\floater_fast_timers.xml: Invalid parameter block for class LLScrollbar
Followed by...
2024-03-09T14:25:05Z WARNING # llcommon/llinitparam.cpp(217) LLInitParam::BaseBlock::validateBlock : Invalid param "page_size"
2024-03-09T14:25:05Z WARNING # llui/lluictrlfactory.h(217) LLUICtrlFactory::createWidgetImpl : D:\Program Files\SecondLifeViewer\skins\default\xui\en\floater_fast_timers.xml: Invalid parameter block for class LLScrollbar
I added the parameters to the XML file using the default values (according to llscrollbar.cpp) of 0 and no longer the warnings are present.