Theme disappeared on downgrading SS version

Questions
1

Silverstripe Version:
4.3.1

I have downgraded from 4.4.1 to 4.3.1, when I run dev/build it does not have any theme just white screen on which dev/build runs successfully. The front-end says the browser is not compatible with SS version. Any idea?

2

I have to ask, why the downgrade? 4.3 is EOL at the end of this year, and the 4.4.x branch brought a bunch of security fixes and updates.

How did you perform the version change? Was it done with composer?

3

Yes I did it via composer. I had issues with images on the latest version. This might be due to my custom module being not compatible with the latest version. I installed a new SS project with 4.3 and everything worked and as soon I upgraded it, the uploaded images were not editable i.e. when I click on an uploaded image the image popup and the form filed disappears without any errors in the console.

4

Can you post your composer.json file? Maybe you’ve ended up with incompatible versions of modules somehow. See WYSIWYG not showing SS4 for a possibly related issue.

5 
"require": {
        "php": ">=5.6.0",
        "silverstripe/recipe-plugin": "^1.2",
        "silverstripe/recipe-cms": "4.3.1@stable",
        "silverstripe/googlesitemaps": "2.1.2",
        "silverstripe/blog": "^3.2",
        "plasticstudio/sitemap": "dev-master",
        "silverstripe/subsites": "2.0.2",
        "tractorcow/silverstripe-fluent": "dev-master",
    },