ComboBox not showing on Dialog load - combobox

Question

I have the following ComboBox declared in a custom Dialog:
<Control Id="EnvironmentCombobox" Type="ComboBox" Sorted="yes" ComboList="yes" Property="ENVIRONMENT" X="25" Y="110" Width="200" Height="15">
<ComboBox Property="ENVIRONMENT">
<ListItem Text="Development" Value="Development" />
<ListItem Text="SIT" Value="SIT" />
<ListItem Text="UAT" Value="UAT" />
<ListItem Text="Production" Value="Production" />
</ComboBox>
</Control>
When I run my installer and get to that dialog, the ComboBox doesn't show until I run my mouse over it. It also appears when if I hit a navigation button. If I leave and come back to the dialog, it is gone again, until I mouse over it or hit a navigation button.
I've tried setting Hidden="no" and increasing the height, but no luck.
Adding full files, per request in comments.
The above is in the EnvironmentDlg:
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<UI>
<Dialog Id="EnvironmentDlg" Width="370" Height="270" Title="[ProductName] Setup">
<!-- Layout. -->
<Control Id="BannerBitmap" Type="Bitmap" X="0" Y="0" Width="370" Height="44" TabSkip="no" Text="!(loc.LicenseAgreementDlgBannerBitmap)" />
<Control Id="BannerLine" Type="Line" X="0" Y="44" Width="370" Height="0" />
<Control Id="BottomLine" Type="Line" X="0" Y="234" Width="370" Height="0" />
<!-- Content. -->
<Control Id="Title" Type="Text" X="15" Y="15" Width="300" Height="15" Transparent="yes" NoPrefix="yes" Text="{\WixUI_Font_Title}Choose environment for [ProductName]" />
<Control Id="InstallText" Type="Text" X="25" Y="70" Width="320" Height="80" Text="Choose the environment to which [ProductName] is being installed." />
<Control Id="EnvironmentCombobox" Type="ComboBox" Sorted="yes" ComboList="yes" Property="ENVIRONMENT" X="25" Y="110" Width="200" Height="15">
<ComboBox Property="ENVIRONMENT">
<ListItem Text="Development" Value="Development" />
<ListItem Text="SIT" Value="SIT" />
<ListItem Text="UAT" Value="UAT" />
<ListItem Text="Production" Value="Production" />
</ComboBox>
</Control>
<!-- Navigation. -->
<Control Id="Back" Type="PushButton" X="180" Y="243" Width="56" Height="17" Text="!(loc.WixUIBack)" />
<Control Id="Next" Type="PushButton" X="236" Y="243" Width="56" Height="17" Default="yes" Text="!(loc.WixUINext)">
<!-- Don't allow user to continue until they have selected an environment. -->
<Condition Action="disable">ENVIRONMENT = ""</Condition>
<Condition Action="enable"><![CDATA[ENVIRONMENT <> ""]]></Condition>
</Control>
<Control Id="Cancel" Type="PushButton" X="304" Y="243" Width="56" Height="17" Cancel="yes" Text="!(loc.WixUICancel)">
<Publish Event="SpawnDialog" Value="CancelDlg">1</Publish>
</Control>
</Dialog>
</UI>
</Fragment>
</Wix>
The sequence is in MyWixUI_Unsecured:
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<UI Id="MyWixUI_Unsecured">
<TextStyle Id="WixUI_Font_Normal" FaceName="Tahoma" Size="8" />
<TextStyle Id="WixUI_Font_Bigger" FaceName="Tahoma" Size="12" />
<TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
<Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
<DialogRef Id="ErrorDlg" />
<DialogRef Id="FatalError" />
<DialogRef Id="FilesInUse" />
<DialogRef Id="MsiRMFilesInUse" />
<DialogRef Id="PrepareDlg" />
<DialogRef Id="ProgressDlg" />
<DialogRef Id="ResumeDlg" />
<DialogRef Id="UserExit" />
<Publish Dialog="ExitDialog" Control="Finish" Event="EndDialog" Value="Return" Order="999">1</Publish>
<Publish Dialog="WelcomeDlg" Control="Next" Event="NewDialog" Value="EnvironmentDlg">1</Publish>
<Publish Dialog="EnvironmentDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg">1</Publish>
<Publish Dialog="EnvironmentDlg" Control="Next" Event="NewDialog" Value="VerifyReadyDlg">1</Publish>
<Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="EnvironmentDlg">1</Publish>
</UI>
<UIRef Id="WixUI_Common" />
</Fragment>
</Wix>

Answer 1

The issue is regarding the Height of InstallText control in EnvironmentDlg.
Change the Height to 25
<Control Id="InstallText" Type="Text" X="25" Y="70" Width="320" Height="25" Text="Choose the environment to which [ProductName] is being installed." />
Full Code:
<?xml version="1.0" encoding="utf-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<UI>
<Dialog Id="EnvironmentDlg" Width="370" Height="270" Title="[ProductName] Setup">
<!-- Layout. -->
<Control Id="BannerBitmap" Type="Bitmap" X="0" Y="0" Width="370" Height="44" TabSkip="no" Text="!(loc.LicenseAgreementDlgBannerBitmap)" />
<Control Id="BannerLine" Type="Line" X="0" Y="44" Width="370" Height="0" />
<Control Id="BottomLine" Type="Line" X="0" Y="234" Width="370" Height="0" />
<!-- Content. -->
<Control Id="Title" Type="Text" X="15" Y="15" Width="300" Height="15" Transparent="yes" NoPrefix="yes" Text="{\WixUI_Font_Title}Choose environment for [ProductName]" />
<Control Id="InstallText" Type="Text" X="25" Y="70" Width="320" Height="25" Text="Choose the environment to which [ProductName] is being installed." />
<Control Id="EnvironmentCombobox" Type="ComboBox" Sorted="yes" ComboList="yes" Property="ENVIRONMENT" X="25" Y="110" Width="200" Height="15">
<ComboBox Property="ENVIRONMENT">
<ListItem Text="Development" Value="Development" />
<ListItem Text="SIT" Value="SIT" />
<ListItem Text="UAT" Value="UAT" />
<ListItem Text="Production" Value="Production" />
</ComboBox>
</Control>
<!-- Navigation. -->
<Control Id="Back" Type="PushButton" X="180" Y="243" Width="56" Height="17" Text="!(loc.WixUIBack)" />
<Control Id="Next" Type="PushButton" X="236" Y="243" Width="56" Height="17" Default="yes" Text="!(loc.WixUINext)">
<!-- Don't allow user to continue until they have selected an environment. -->
<Condition Action="disable">ENVIRONMENT = ""</Condition>
<Condition Action="enable"><![CDATA[ENVIRONMENT <> ""]]></Condition>
</Control>
<Control Id="Cancel" Type="PushButton" X="304" Y="243" Width="56" Height="17" Cancel="yes" Text="!(loc.WixUICancel)">
<Publish Event="SpawnDialog" Value="CancelDlg">1</Publish>
</Control>
</Dialog>
</UI>
</Fragment>
</Wix>
I will suggest you using WixEdit control for designing UI