The rollmark with the three crowns within the shield indicates Umarex. I think Walther's rollmark is a stag.
I've never had good luck with Umarex firearms either. I bought the S&W M&P 22 assuming it was a Walther. When cleaning it, I noticed the Umarex rollmark. At first, I was really upset about it.
My M&P 22 has fired 4 bricks of bulk ammo and 200 rounds of CCI Mini-Mag without issue, so I'm not that upset anymore. S&W claims that Walther manufacturers the M&P 22 to S&W's design & specification.
I guess that's the factor that makes this particular Umarex manufactured firearm different from the others, Umarex didn't design it.
I still hate Umarex with a passion.