Sometimes errors, sometimes works, haven't found any sort of pattern.

I disabled all addons except Leatrix Maps (v9.2.41), I enabled the taint log and got the error below; the LUA error is further down. Disabling LM I haven't experienced any issues.

Taintlog:
10/10 16:33:07.373 Global variable UIDROPDOWNMENU_MENU_LEVEL tainted by Leatrix_Maps - Interface\SharedXML\UIDropDownMenu.lua:37
10/10 16:33:07.373 securecall()
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:73 UIDropDownMenu_Initialize()
10/10 16:33:07.373 Interface\FrameXML\EasyMenu.lua:21 EasyMenu()
10/10 16:33:07.373 Interface\FrameXML\LFGList.lua:2619
10/10 16:33:07.373 Execution tainted by Leatrix_Maps while reading UIDROPDOWNMENU_MENU_LEVEL - Interface\SharedXML\UIDropDownMenu.lua:864 UIDropDownMenu_GetSelectedID()
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:539 UIDropDownMenu_AddButton()
10/10 16:33:07.373 Interface\FrameXML\EasyMenu.lua:30 initFunction()
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:78 UIDropDownMenu_Initialize()
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:1075 ToggleDropDownMenu()
10/10 16:33:07.373 Interface\FrameXML\EasyMenu.lua:22 EasyMenu()
10/10 16:33:07.373 Interface\FrameXML\LFGList.lua:2619
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:916 UIDropDownMenuButton_OnClick()
10/10 16:33:07.373 An action was blocked because of taint from Leatrix_Maps - SendReport()
10/10 16:33:07.373 Interface\FrameXML\ReportFrame.lua:171 ReportFrame:SendReport()
10/10 16:33:07.373 Interface\FrameXML\ReportFrame.lua:75 ReportFrame:InitiateReportInternal()
10/10 16:33:07.373 Interface\FrameXML\ReportFrame.lua:427
10/10 16:33:07.373 ReportFrame:SetAttribute()
10/10 16:33:07.373 Interface\FrameXML\ReportFrame.lua:52 ReportFrame:InitiateReport()
10/10 16:33:07.373 Interface\FrameXML\LFGList.lua:3281 LFGList_ReportAdvertisement()
10/10 16:33:07.373 Interface\FrameXML\LFGList.lua:3313 func()
10/10 16:33:07.373 Interface\SharedXML\UIDropDownMenu.lua:918 UIDropDownMenuButton_OnClick()
10/10 16:33:07.373 DropDownList1Button4:OnClick()

LUA error:
5x [ADDON_ACTION_FORBIDDEN] AddOn 'Leatrix_Maps' tried to call the protected function 'SendReport()'.
[string "@!BugGrabber\BugGrabber.lua"]:519: in function <!BugGrabber\BugGrabber.lua:519>
[string "=[C]"]: in function SendReport' [string "@FrameXML\ReportFrame.lua"]:171: in function SendReport'
[string "@FrameXML\ReportFrame.lua"]:75: in function InitiateReportInternal' [string "@FrameXML\ReportFrame.lua"]:427: in function <FrameXML\ReportFrame.lua:413> [string "=[C]"]: in function SetAttribute'
[string "@FrameXML\ReportFrame.lua"]:52: in function InitiateReport' [string "@FrameXML\LFGList.lua"]:3281: in function LFGList_ReportAdvertisement'
[string "@FrameXML\LFGList.lua"]:3313: in function func' [string "@SharedXML\UIDropDownMenu.lua"]:918: in function UIDropDownMenuButton_OnClick'
[string ":OnClick"]:1: in function <[string ":OnClick"]:1>

https://github.com/leatrix/leatrix-maps-wrath/issues/56

I know you are reporting ads in group finder rather than players in a battleground but it's the same sort of error.

Next time you see the error, try /reload and see if that fixes it temporarily.

Not enabling any of the zoom settings at all during your current login session might help but if you use them, you probably find them more useful than the ability to report ads.

These errors are the main reason why LTM was split from LTP (it was originally included with LTP). Blizzard doesn't want to fix the issues with the game code so we're left with what we have.