Have I not understood what "several" means?

Solution 1:

There are two uses of 'several' in one sentence here:

...out of the 42 million bitcoin wallet addresses on the blockchain, several are no longer in use and that many users occupy several wallets.

Let's examine the context. The OP did not state the origin of the text, but I have found it on a site called 'bitcoinjournal.com', which proudly states that it is 'trusted by over 100,000 blockchain investors'. I note in passing that this is a small percentage of 42 million.

The paragraph is at the end of an article headed 'How Many People Use Bitcoin in 2020?', which examines estimates from various sources and in a section titled 'So, How Many People Use Bitcoin? Here’s the Math!', attempts to answer that question. This title hardly suggests a rigorous approach, and the opening section blatantly, and ungrammatically, contradicts itself:

In light of the limited data and the impossibility of accurately determining the number of bitcoin users around the world, we can safely estimate that there will be around 25 million users globally.

The next paragraph contains the text in the OP, and seems to be guessing that, of 42 million wallet addresses, 25 million represent a 'fair estimate'. The phrase 'several million' (users not serviced by Coinbase) is used to justify this.

This it seems that the writer understands the meaning of 'several' but wrote, or edited, the article in haste, and should have placed 'million' after the first 'several' in the quoted sentence.