For discover cards, the CLI approval seems to be limited to 1 per a statement cycle. I requested a CLI in the last month once and it was accepted. A few days later, my second request was rejected. I waited for the next monthly statement, and I requested a CLI again and it was accepted. Each time ~1200-2000$ increase. The card is starting with a small CL, growing slowly while it reaches an excellent level in a long term.
Fico8: EX~EQ~TU~840 (12 month goal~850).