Recently I've had delivery issues with Thunderbird. That makes me rethink my use of it. I sent the same email from the same address to the same recipient once

Recently I've had delivery issues with Thunderbird. That makes me rethink my use of it. I sent the same email from the same address to the same recipient once with Thunderbird on Windows, once with Apple Mail on iOS. The one with Thunderbird was silently dropped (not even reaching the spam folder), the one sent with Apple Mail reached the inbox without issue. I've had that same issue with 2 different recipient companies. And yes, my address passes SPF, DKIM, has a strict DMARC, and isn't in any blacklist (uses iCloud+ as host).