"I like it very much."
Translation:Taitníonn sé go mór liom.
Sorry I misinterpreted. I hope a grammarian of Irish will answer your question. I sometimes use Google to see how prevalent a phrase might be on the internet. This phrase: "go mór liom." got 38,800 hits on Google.ie and the contrasting phrase "liom go mór." got 36,000 results. Now ungrammatical things are posted on the internet all the time. However, this data makes me think you might be onto something?!
I was complaining once to a learning speaker who has reached a high degree of fluency about how Duoling doesn't always proceed in stepwise fashion and this can cause these shocks, like the one you experienced. She said the shocks can be useful as they cause you to remember the new item.
I don't know about remembering the item. If anything, the shock forced me to accommodate a whole new paradigm for remembering vocabulary. I had begun to believe that a certain pattern exists for sentence formation in Irish, only to be shown that it doesn't always work that way. Now I have to learn a whole new pattern. Challenging but scary.
I remember when my youngest brother was a toddler. He used to say he would do such and such "until we get home". He meant that he would do it when he got home. He didn't understand the correct use of the word "until". That took a whole other set of responses to learn. This experience is like that one.
Do you understand why someone would interpret your "Is maith liom an-mór" as "I like very big"?
If so, do you understand why it wouldn't be understood as "I like it very much"? Apart from the missing pronou ("it"), an-mhór (an- lenites) means "very big" not "very much".
Duolingo has a number of exercises using taitnionn X le Y to mean "Y likes X" or "Y enjoys X" or "X pleases Y", introduced as early as Verbs: Present 1 - it shouldn't be much of a shock by the time you get to the Adverbs skill.