This is because of the use of the ampersand &
in your statement. It needs to be escaped as &
to stop XSTL trying to treat the following characters as an entity.
Try this instead:
<xsl:value-of select="concat('https://mysite/_layouts/listform.aspx?PageType=4&ListId={listiD}&ID=',@ID,'&ContentTypeID=0x0100B0D8940B0260E54DA1649533F29D58D7')"/>