How to troubleshoot when the onGatheringStateChange function returns very slowly？

[bestxpp]

        pc_->onGatheringStateChange([this, pc = pc_](rtc::PeerConnection::GatheringState state) {
			std::ostringstream oss;
			oss << state;
			LOG_INFO("Gathering State: {}", oss.str());

			if (state == rtc::PeerConnection::GatheringState::Complete) {
				auto		   description = pc->localDescription();
				nlohmann::json message	   = {{"type", description->typeString()}, {"sdp", std::string(description.value())}};
				// std::cout << message << std::endl;
				nlohmann::json sendOffer = {{"type:", wb_type::offer}, {"data", message.dump()}};
				LOG_INFO("send: {}", sendOffer.dump());
				MyWebSocket::get().send(sendOffer.dump());
			}
		});

the onGatheringStateChange function returns very slowly,It takes 20 to even 40 seconds to gather ICE information.
coturn and my application are running on the same host; the difference is that my application is running in a Docker container, while coturn is running on the host machine

[paullouisageneau]

It means one of your ICE servers is not reachable, so gathering done is only triggered after it times out.