Unknown encryption algorithm \"undefined\"

[waclaw66]

Describe the bug
A message has been deleted from Element Android. Element Web shows then:

Decrypted source:

{
  "type": "m.room.message",
  "content": {
    "msgtype": "m.bad.encrypted",
    "body": "** Unable to decrypt: Unknown encryption algorithm \"undefined\". **"
  }
}

Source:

{
  "type": "m.room.encrypted",
  "sender": "@waclaw:bolesiny.net",
  "content": {},
  "origin_server_ts": 1613727587425,
  "unsigned": {
    "age": 252887558,
    "transaction_id": "m1613727587419.1",
    "redacted_because": {
      "type": "m.room.redaction",
      "sender": "@waclaw:bolesiny.net",
      "content": {},
      "redacts": "$NM2UWY7FBYl2PChvnPodHLEBFEC_2RW--w4A6zFcy9A",
      "origin_server_ts": 1613898020667,
      "unsigned": {
        "age": 82453640
      },
      "event_id": "$LZhXpMqqkgLK7_a2vg1P9sKCUEuLxwMoawfWR5U8tbo",
      "room_id": "!szATDhOAazzMLQFKTe:bolesiny.net"
    }
  },
  "event_id": "$NM2UWY7FBYl2PChvnPodHLEBFEC_2RW--w4A6zFcy9A",
  "room_id": "!szATDhOAazzMLQFKTe:bolesiny.net"
}

Not sure whether this is a bug of Element Android or Element Web.
Session keys have been properly in sync before.
Request of new sync from that message has no effect and shows following in console...

Error requesting key for event DOMException: Data provided to an operation does not meet requirements. KeyboardShortcuts.tsx:277:22
    n KeyboardShortcuts.tsx:277
    methodFactory logger.ts:45
    requestRoomKey index.js:2888
    (Async: promise callback)
    requestRoomKey index.js:2888
    cancelAndResendKeyRequest event.js:181
    cancelAndResendEventRoomKeyRequest client.js:1154
    F EventTile.js:55
    s olm.js:100
    p olm.js:100
    _ olm.js:100
    _ olm.js:101
    React 5
    q olm.js:119
    React 2
    unstable_runWithPriority scheduler.production.min.js:13
    React 3

To Reproduce
Steps to reproduce the behavior:

1. Create a message containing an URL from Element Web
2. Try to Redact it from Element Android after few days.
3. A new message is created instead of redaction (probably another bug)
4. Delete the original message from Element Android.
5. See error on Element Web

Expected behavior
"Message deleted" should be shown without any warning.

Smartphone:

• Device: Xiaomi Mi 9T
• OS: Android 10

Additional context

• App version and store: Element Web 1.7.21 on Firefox, Element Android 1.0.17 from GStore
• Homeserver: self hosted Synapse 1.27

[waclaw66]

Still happens for every deleted message. Seems similar to matrix-org/matrix-js-sdk#1648.
Element Android doesn't show any error message though.