If the lag detector's logger is set to `DEBUG` then the master will capture the hot threads on the lagging node and report them in its logs. However it's quite possible for this log message to be many kB in size, and log messages are apparently truncated at 10kB by default.

We should find another way to report this information to avoid hitting this size limit. Perhaps simply split the hot threads output up across multiple log messages, or perhaps find a different way to report it.
server/src/main/java/org/elasticsearch/cluster/coordination/LagDetector.java
private final DiscoveryNode discoveryNode;
        private final AtomicLong appliedVersion = new AtomicLong();
        NodeAppliedStateTracker(final DiscoveryNode discoveryNode) {
            this.discoveryNode = discoveryNode;
        }
        void increaseAppliedVersion(long appliedVersion) {
            long maxAppliedVersion = this.appliedVersion.accumulateAndGet(appliedVersion, Math::max);
            logger.trace("{} applied version {}, max now {}", this, appliedVersion, maxAppliedVersion);
        }
        boolean appliedVersionLessThan(final long version) {
            return appliedVersion.get() < version;
        }
        @Override
        public String toString() {
            return "NodeAppliedStateTracker{" + "discoveryNode=" + discoveryNode + ", appliedVersion=" + appliedVersion + '}';
        }
        void checkForLag(final long version) {
            if (appliedStateTrackersByNode.get(discoveryNode) != this) {
                logger.trace("{} no longer active when checking version {}", this, version);