diff --git a/src/main/kotlin/ch/uzh/ifi/access/config/SecurityConfig.kt b/src/main/kotlin/ch/uzh/ifi/access/config/SecurityConfig.kt
index b304c81..b3a8c43 100644
--- a/src/main/kotlin/ch/uzh/ifi/access/config/SecurityConfig.kt
+++ b/src/main/kotlin/ch/uzh/ifi/access/config/SecurityConfig.kt
@@ -28,7 +28,9 @@ import org.springframework.web.filter.CommonsRequestLoggingFilter
 import java.nio.file.Path
 import java.time.Duration
 import java.time.Instant
+import java.time.LocalDate
 import java.time.LocalDateTime
+import java.time.ZoneId
 
 
 @AllArgsConstructor
@@ -159,13 +161,16 @@ class AuthenticationSuccessListener(
             else {
                 try {
                     val lastSync  = currentAttributes["roles_synced_at"]!!.first()
-                    val timeStamp = lastSync.substring(0, Math.min(lastSync.length, lastSync.indexOf('.') + 4)) + "Z"
-                    val dateTime = Instant.parse(timeStamp)
-                    val now = Instant.now()
-                    if (Duration.between(dateTime, now).toMinutes() > 10) {
+                    val lastSyncInstant = LocalDateTime.parse(lastSync)
+                    val now = LocalDateTime.now()
+                    val diff = Duration.between(lastSyncInstant, now).toMinutes()
+                    if (diff > 10) {
                         logger.debug { "syncing $username to courses after more than 10min" }
                         courseService.updateStudentRoles(username)
                     }
+                    else {
+                        logger.debug { "only $diff minutes elapsed since last sync of $username at ${lastSync} (now: $now)" }
+                    }
                 } catch (e: Exception) {
                     logger.debug { "problem ($e, ${e.stackTrace}) with sync calculation; syncing $username to courses anyway" }
                     courseService.updateStudentRoles(username)
diff --git a/src/main/kotlin/ch/uzh/ifi/access/service/RoleService.kt b/src/main/kotlin/ch/uzh/ifi/access/service/RoleService.kt
index 2ec565d..ce94b94 100644
--- a/src/main/kotlin/ch/uzh/ifi/access/service/RoleService.kt
+++ b/src/main/kotlin/ch/uzh/ifi/access/service/RoleService.kt
@@ -144,6 +144,7 @@ class RoleService(
     fun updateStudentRoles(course: Course, registrationIDs: Set<String>, username: String) {
         val role = accessRealm.roles()[Role.STUDENT.withCourse(course.slug)]
         val rolesToAdd = listOf(role.toRepresentation())
+        logger.debug { "registered students for ${course.slug}: $registrationIDs"}
         logger.debug { "B: updating roles for ${username} (roles to add: ${rolesToAdd})"}
         logger.debug { "Searching if ${username} is in ${role.getUserMembers(0, -1).size} members of ${role} in keycloak" }
         role.getUserMembers(0, -1)