This has happened to me several times -- if you revive 3 people very quickly, then the game blocks you from radio usage due to spamming. This is because your character issues 3 (or 4?) messages automatically whenever you revive someone (hold on, it's charging, clear, ok your good to go, etc), so after 9 of these in a row (ie. 3 quick revives), your considered radio spamming!
Reviving triggers radio spam block
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