First off, if you needed to file Schedule 1, then you should have answered "yes" to the question at the top of the page - "At any time during 2019, did you receive, sell, send, exchange, or otherwise acquire any financial interest in any
virtual currency?" - since you did some of that. This doesn't affect your taxes directly and doesn't care if you made money or not.
Second, you definitely should have reported it (regardless of gain or loss), and it's possible the IRS will send you a notice later on. You may or may not have any consequences of this, depending on the financial details of your tax return. And yes, even file if you think it's a loss - it's still important to do so.
I'm not sure that it's definite how the IRS handles virtual currency transactions - nothing I can find is explicit - but assuming they treat them like stocks, you may owe tax on the profit you earned in 2019 over 2017 even though you repurchased. If the money went the other way - if it was a loss 2017->2019 - it would be different, or at least may be different (it's also unclear if wash sale rules apply to BTC), but they don't apply on profits in any event.
As such, you probably had a ~$3000 profit on the first transaction, and you owe taxes on that. Depending on your income, that could range from $0 to $450 most likely (as it's a long term gain), or as much as $600 if your income is high enough to hit the 20% CG rate.
BTC Purchase Sale Profit
1 $6000 $9000 $3000
2 $9000 - -
Maybe the table above helps - that's how the IRS sees your transaction. They also don't care about the BTC "amounts" - first one is a buy [something] for $6k, sell [something] for $9k; second is buy [something else] for $9k.
Do also consider US / Euro fluctuations here, both between 2017 -> 2019 and 2019 -> 2019. I'm not 100% sure how those are handled, but it's important to think about it and find out.
Finally, I don't know how your purchasing this while not in the US and not subject to US Tax laws affects the basis. It may, or may not. Look into it, or more likely ask a tax pro (and not someone working for H&R Block, but an actual tax accountant).
My recommendation would be to consult a tax pro if you can, as this is enough money that you'll end up owing some penalties. They can help make sure you have this exactly right and minimize the consequences to you. Also, given your other question, it sounds like you might have another thing to discuss with the IRS agent on the phone - do the same thing, call to ask to have them waived, and explain that you thought it was a wash but you learned from discussing with some folks on the internet it isn't.