BFI Extended Signature - Search String Based

Content Authoring SUA Signatures
2

Can you try below signature?

<MultipleInstance>
	<Iterator export="true" name="INSTALL_PATH">
		<FindFilePathEx name="MYFILE.txt"/>
	</Iterator>
	<Instance>
		<Variable export="false" name="file_read">
			<ReadFile path="$(INSTALL_PATH)MYFILE.txt"/>
		</Variable>
		<Variable name="IS_INSTALLED">
			<Contains inputString="$(file_read)" position="contains" searchedString="MYAPP_version=1.3"/>
		</Variable>
		<Condition withVariable="IS_INSTALLED">
			<Action do="SKIP" onValue="false"/>
		</Condition>
	</Instance>
</MultipleInstance>

Check below link since it contains a post to debug the signature issue