diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index f8ce23a3f..d295c054a 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -264,11 +264,14 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
         await Promise.all([
             (async () => {
                 // share keys with devices that we already have a session for
+                logger.debug(`Sharing keys with existing Olm sessions in ${this._roomId}`);
                 await this._shareKeyWithOlmSessions(
                     session, key, payload, olmSessions,
                 );
+                logger.debug(`Shared keys with existing Olm sessions in ${this._roomId}`);
             })(),
             (async () => {
+                logger.debug(`Sharing keys with new Olm sessions in ${this._roomId}`);
                 const errorDevices = [];
 
                 // meanwhile, establish olm sessions for devices that we don't
@@ -319,8 +322,10 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                 } else {
                     await this._notifyFailedOlmDevices(session, key, errorDevices);
                 }
+                logger.debug(`Shared keys with new Olm sessions in ${this._roomId}`);
             })(),
             (async () => {
+                logger.debug(`Notifying blocked devices in ${this._roomId}`);
                 // also, notify blocked devices that they're blocked
                 const blockedMap = {};
                 for (const [userId, userBlockedDevices] of Object.entries(blocked)) {
@@ -336,6 +341,7 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                 }
 
                 await this._notifyBlockedDevices(session, blockedMap);
+                logger.debug(`Notified blocked devices in ${this._roomId}`);
             })(),
         ]);
     };
@@ -348,6 +354,11 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
     // first wait for the previous share to complete
     const prom = this._setupPromise.then(prepareSession);
 
+    // Ensure any failures are logged for debugging
+    prom.catch(e => {
+        logger.error(`Failed to ensure outbound session in ${this._roomId}`, e);
+    });
+
     // _setupPromise resolves to `session` whether or not the share succeeds
     this._setupPromise = prom.then(returnSession, returnSession);
 
@@ -840,24 +851,41 @@ MegolmEncryption.prototype.prepareToEncrypt = function(room) {
         // We're already preparing something, so don't do anything else.
         // FIXME: check if we need to restart
         // (https://github.com/matrix-org/matrix-js-sdk/issues/1255)
+        const elapsedTime = Date.now() - this.encryptionPreparationMetadata.startTime
+        logger.debug(
+            `Already started preparing to encrypt for ${this._roomId} ` +
+            `${elapsedTime} ms ago, skipping`,
+        );
         return;
     }
 
     logger.debug(`Preparing to encrypt events for ${this._roomId}`);
 
+    this.encryptionPreparationMetadata = {
+        startTime: Date.now(),
+    };
     this.encryptionPreparation = (async () => {
-        const [devicesInRoom, blocked] = await this._getDevicesInRoom(room);
+        try {
+            logger.debug(`Getting devices in ${this._roomId}`);
+            const [devicesInRoom, blocked] = await this._getDevicesInRoom(room);
 
-        if (this._crypto.getGlobalErrorOnUnknownDevices()) {
-            // Drop unknown devices for now.  When the message gets sent, we'll
-            // throw an error, but we'll still be prepared to send to the known
-            // devices.
-            this._removeUnknownDevices(devicesInRoom);
+            if (this._crypto.getGlobalErrorOnUnknownDevices()) {
+                // Drop unknown devices for now.  When the message gets sent, we'll
+                // throw an error, but we'll still be prepared to send to the known
+                // devices.
+                this._removeUnknownDevices(devicesInRoom);
+            }
+
+            logger.debug(`Ensuring outbound session in ${this._roomId}`);
+            await this._ensureOutboundSession(devicesInRoom, blocked, true);
+
+            logger.debug(`Ready to encrypt events for ${this._roomId}`);
+        } catch (e) {
+            logger.error(`Failed to prepare to encrypt events for ${this._roomId}`, e);
+        } finally {
+            delete this.encryptionPreparationMetadata;
+            delete this.encryptionPreparation;
         }
-
-        await this._ensureOutboundSession(devicesInRoom, blocked, true);
-
-        delete this.encryptionPreparation;
     })();
 };