The Miracle, Every Breaking Wave, and Song for Someone were released to radio as singles, but none was ever sold in the UK as a physical single or a paid download.
I'm pretty sure the UK singles chart calculation has included streaming since Summer 2014, so SOI album cuts would have been eligible for the chart when they hit Spotify in October of that year, but by then the free iTunes release had been out for a month. Apple Music hadn't even launched at the time, so the album was only available as a free download for the first few weeks, which doesn't count as a "sale" for chart purposes. The album did stream initially on Beats Music, but I believe that was US only?
Anyway, The Miracle didn't chart because it was initially only available as a free download as part of the album.
The single version of Every Breaking Wave was a free download on U2.com. There was never a download for sale or a streaming single (other than the U2.com stream).
Song for Someone was released as a streaming single on Spotify in September 2015, so it would have been eligible to chart, it just didn't. It wasn't noticeably different from the album version, anyway.
So maybe that makes Song for Someone U2's worst performing chart-eligible single, failing to chart at all?