Was just copying a large block of mixed HTML/PHP for a Plates template between files and received an exception in VS. Exception details from activity log are below. Result was no formatting/highlighting for text in file after paste. Issue was resolved after I closed and re-opened the file in VS.
<entry>
<record>1635</record>
<time>2019/11/13 10:40:56.782</time>
<type>Error</type>
<source>Editor or Editor Extension</source>
<description>System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: span

at Microsoft.VisualStudio.Text.Implementation.TrackingSpan..ctor(ITextVersion version, Span span, SpanTrackingMode trackingMode)

at Microsoft.VisualStudio.Text.Implementation.TextVersion.CreateTrackingSpan(Int32 start, Int32 length, SpanTrackingMode trackingMode)

at Microsoft.VisualStudio.Text.Implementation.BaseSnapshot.CreateTrackingSpan(Int32 start, Int32 length, SpanTrackingMode trackingMode)

at Microsoft.WebTools.Languages.Html.Editor.Classification.HtmlClassifier.OnTextBufferChanged(Object sender, TextContentChangedEventArgs e)

at Microsoft.VisualStudio.Text.Utilities.GuardedOperations.RaiseEvent[TArgs](Object sender, EventHandler1 eventHandlers, TArgs args)
--- End of stack trace from previous location where exception was thrown ---

at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)</description>
</entry>