diff --git a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
index 51d6be6e..9ce9e313 100644
--- a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
+++ b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
@@ -96,21 +96,28 @@ public class SignalAccountFiles {
         return this.initManager(number, accountPath);
     }
 
-    public Manager initManagerByAci(String aciStr) throws IOException, NotRegisteredException, AccountCheckException {
-        final var aci = ACI.parseOrThrow(aciStr);
-        final var accountPath = accountsStore.getPathByAci(aci);
-        if (accountPath == null) {
-            throw new NotRegisteredException();
-        }
+    public String getAccountNumberByAci(final String aciStr) throws IOException {
         final var accounts = accountsStore.getAllAccounts();
         final var account = accounts.stream()
                 .filter(a -> aciStr.equals(a.uuid()))
                 .findFirst()
-                .orElseThrow(NotRegisteredException::new);
-        if (account.number() == null) {
+                .orElse(null);
+        if (account == null || account.number() == null) {
+            return null;
+        }
+        return account.number();
+    }
+
+    public Manager initManagerByAci(String aciStr) throws IOException, NotRegisteredException, AccountCheckException {
+        final var phoneNumber = getAccountNumberByAci(aciStr);
+        if (phoneNumber == null) {
             throw new NotRegisteredException();
         }
-        return this.initManager(account.number(), accountPath);
+        final var accountPath = accountsStore.getPathByNumber(phoneNumber);
+        if (accountPath == null) {
+            throw new NotRegisteredException();
+        }
+        return this.initManager(phoneNumber, accountPath);
     }
 
     private Manager initManager(
diff --git a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
index c4d042e5..b943a007 100644
--- a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
+++ b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
@@ -114,11 +114,29 @@ public class MultiAccountManagerImpl implements MultiAccountManager {
             } catch (NotRegisteredException e) {
                 // Not a valid phone number or not registered yet, try ACI
                 logger.debug("Manager not found by number, trying ACI: {}", identifier);
-            } catch (IOException | AccountCheckException e) {
+            } catch (IOException | IllegalArgumentException | AccountCheckException e) {
                 logger.warn("Failed to load new manager by number: {}", identifier, e);
                 return null;
             }
 
+            // Before trying to initByAci (which would try to re-open an already-locked file),
+            // check if this UUID corresponds to an already-loaded manager
+            try {
+                final var phoneNumber = signalAccountFiles.getAccountNumberByAci(identifier);
+                if (phoneNumber != null) {
+                    final var existingManager = managers.stream()
+                            .filter(m -> m.getSelfNumber().equals(phoneNumber))
+                            .findFirst()
+                            .orElse(null);
+                    if (existingManager != null) {
+                        logger.debug("Found already loaded manager for ACI: {}", identifier);
+                        return existingManager;
+                    }
+                }
+            } catch (IOException e) {
+                logger.warn("Failed to lookup ACI in accounts: {}", identifier, e);
+            }
+
             // Try to load by ACI (useful for SSE endpoint with ?account=<UUID>)
             try {
                 final var newManager = signalAccountFiles.initManagerByAci(identifier);
@@ -126,7 +144,7 @@ public class MultiAccountManagerImpl implements MultiAccountManager {
                 return newManager;
             } catch (NotRegisteredException e) {
                 logger.debug("Manager not found by ACI: {}", identifier);
-            } catch (IOException | AccountCheckException e) {
+            } catch (IOException | IllegalArgumentException | AccountCheckException e) {
                 logger.warn("Failed to load new manager by ACI: {}", identifier, e);
             }
 
diff --git a/src/main/java/org/asamk/signal/util/Util.java b/src/main/java/org/asamk/signal/util/Util.java
index 585c5690..76e41fa7 100644
--- a/src/main/java/org/asamk/signal/util/Util.java
+++ b/src/main/java/org/asamk/signal/util/Util.java
@@ -79,7 +79,7 @@ public class Util {
         for (var param : params) {
             final var paramParts = param.split("=", 2);
             var name = URLDecoder.decode(paramParts[0], StandardCharsets.UTF_8);
-            var value = paramParts.length == 1 ? null : URLDecoder.decode(paramParts[1], StandardCharsets.UTF_8);
+            var value = paramParts.length == 1 ? null : URLDecoder.decode(paramParts[1].replace("+", "%2B"), StandardCharsets.UTF_8);
             map.put(name, value);
         }
         return map;