Apparent rate limiting on send (with attachments)

[thedeadliestcatch]

I've been observing the following behavior:

signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:04:53 | 201 |         10m2s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:04:53 | 201 |         9m53s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:04:53 | 201 |        10m22s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:44 | 201 |        10m32s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:45 | 201 |         9m34s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:45 | 201 |        10m13s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:45 | 201 |         9m37s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:45 | 201 |         8m30s |      xxx | POST     "/v2/send"
signal-cli-rest-api-1  | [GIN] 2024/06/27 - 20:06:45 | 201 |         9m33s |      xxx | POST     "/v2/send"

Messages are timestamped and delivered on average 10 minutes later than they should be. No errors in the log or messages related to rate limiting.

json-rpc is used as the backend.

Another user reported this issue here: bbernhard/signal-cli-rest-api#545

It seems I was mistaken to dismiss it as a signal-cli-rest-api issue. I observe exactly the same problem as @uriinf.