The reason for a certain song or songs to appear grayed out, and where you can't click on the song to play it, is because Spotify has either removed this song, or it is not available in your country. I too live in the U.S. and a favorite song of mine was recently removed.
OK. I'll play the game. These tracks are in my playlist but they are greyed out & won't play. I give the artist, album name, track name, date added to playlist, comment (sometimes).
Albert Collins, Live at Rockpalast (Live at Dortmund Westfallenhalle 2, 26.11.1980), Cold Cuts - Live, 2016-08-28, All 12 other tracks on the album play fine. B.B. King, B.B. King & Friends, 5 tracks are grey: Tired of Your Jive, Need Your Love So Bad, There Must Be a Better World Somewhere, Never Make Your Move Too Soon, Rock This House, 7 other tracks of the album play fine, 2016-08-28 B.B. King, Ladies and Gentleman, Mr. B.B. King, 13 tracks are grey, 17 tracks play fine, 2016-09-14, That's too many tracks to list individually. Thank me. Buddy Guy, Can't Quit the Blues, 6 tracks are grey: The Way You Been Treating Me - Demo, When You See the Tears from My Eyes - Live, She Suits Me to a T, DJ Play My Blues, I Can't Be Satisfied - Live, First Time I Met the Blues - Live, 18 other tracks on the album play fine, 2016-08-28 Buddy Guy, Skin Deep Deluxe Version, Take Out Some Insurance, 2016-08-28, 14 other tracks on the album play fine. Cream, BBC Sessions, 13 tracks are grey, Steppin' Out plays fine, 2016-08-23 Cream, Those Were the Days, 11 tracks are grey, 21 tracks play fine, 2016-08-23 Creedence Clearwater Revival, Bayou Country (40th Anniversary Edition), Bootleg - Alternate Track, Born on the Bayou - Live in London, Proud Mary - Live in Stockholm, Crazy Otto - Live at the Filmore, 2016-08-23, 4 other tracks on the album play fine. Creedence Clearwater Revival, Pendulum (40th Anniversary Edition), Hey Tonight - Live in Hamburg, 2016-08-23, 9 other tracks on the album play fine. Heart, The Essential Heart, Tell it Like it Is, Unchained Melody - Live, Never, Nothin' At All, If Looks Could Kill, You're the Voice - Live, 2016-08-28, 11 other tracks on the album play fine. Heart, Heart, The Wolf, All Eyes, Nobody Home, Nothin' At All, What He Don't Know, Shell Shock, 2016-08-28, 2 other tracks on the album play fine. Heart, Rock the House Live!, Shell Shock - Live at the Centrum/1980, 2016-08-28, 13 other tracks on the album play fine. Heart, Strange Euphoria, Dreamboat Annie (Fantasy Child) + Dreamboat Annie Reprise - 2012 Remaster, Under the Sky - Demo, Never - Live, 2016-08-28, 26 other tracks on the album play fine. Howlin' Wolf + Muddy Waters, Muddy & the Wolf, Highway 49, The Red Rooster, 2016-08-28, 11 other tracks on the album play fine. Jefferson Airplane, 2400 Fulton Street, My Best Friend, J.P.P. McStep B. Blues, Volunteers, The Levi Commercials, 2016-08-28, 32 other tracks on the album play fine. The Mamas & The Papas, Historic Performances Recorded at the Monterey International Pop Festival (Live), 7 tracks are grey, 2016-08-23 Maná, Dónde jugarán los niños (bonus remixes version), Cómo te deseo (video), La chula (remix version), 2016-08-26, 10 other tracks on the album play fine. Muddy Waters, The Lost Tapes, Muddy's Introduction to 19 Years Old - Live, 2016-08-28, 10 other tracks on the album play fine. Robert Cray, Bad Influence, 9 tracks are grey, 3 tracks play fine, 2016-09-08 Robert Cray, The Definitive Collection, Bad Influence, 2016-08-28, This is a compilation album of 16 tracks, most of which I have on my playlist from other albums. But this is the only track on this album that is grey. The rest play fine. Robert Cray, False Accusations, 1 track (Playin' in the Dirt) plays fine, 8 other tracks are grey, 2016-09-08 Rolling Stones, Jump Back, This is a compilation album of 18 tracks, 5 are grey, the rest play fine. The ones actually on my playlist that I didn't filter out as duplicates are Mixed Emotions - Remastered, Miss You - Remastered 1993, both of which are grey, 2017-06-02 Rolling Stones, Shine a Light, This is from a live performance in 2006 at the Beacon Theater. All 24 tracks on the album are grey. 2016-08-23 Roy Buchanan, Live at My Father's Place, all 10 songs on the album are grey, 2016-08-28 Roy Buchanan, Live at Rockpalast (Live at Markthalle Hamburg 24.02.1985), Only Wayfaring Pilgrim plays fine. The other 12 tracks on the album are grey. 2016-08-28
All of these tracks played fine on the days I added them to my playlist, and for some unknown time after. Something has happened in the interim. But for the life of me, I can't justify any of these blocked tracks. In each case, I have lots of other content from the same artist that plays fine. And as you can see, most of the blocked tracks are from albums that mostly play fine. So I don't think the "not available in your country" excuse is valid. I'm in the US & most of these performers are domestic so all their content should be available to me. Even the "foreign" acts I've mentioned (Cream, Maná, The Stones) take up a significant portion of my playlist, just to point out that they are mostly not blocked despite not being domestic.
You may note a discrepancy between my track counts & the actual track counts on certain albums. This is because I spent a lot of time filtering out duplicates. A lot of acts put the exact same performance of a given track on multiple albums. So I tried to figure out which one was best. Sometimes a remastering improved the song. Sometimes I just arbitrarily picked one & deleted the rest of the duplicates. So my track counts reflect the tracks I left in my playlist.
I have found advice online that claims if I go to %appdata% & look in Roaming & Local, I'll find Spotify cache. The claim is that deleting the cache should ungrey the grey tracks. Deleting the cache doesn't make any difference. One thing the advice doesn't make clear is that you should do this when Spotify is closed. Not running. Doesn't matter. The cache directory structures reappear when you next open Spotify, which is fine, but the grey tracks remain grey.
And this is a fresh install.
You can see my playlist (it's public) as Wild Willy's Playlist. Not very imaginative but it works.