Back to knowledge base

Why am I getting backend errors when I use multiple Magento admin tabs?

Tags: Magento error, Admin error, Magento admin, Backend, Admin tabs
If you open several Magento 2 admin tabs and suddenly experience issues like:
  • 503 Service Unavailable  
  • Actions failing without explanation  
  • Extensions (including WriteText.ai) stopping mid-process  
  • Tabs randomly crashing or hanging  

…it may feel like something is wrong with the browser, the tab, or even the extension you are using.
In many cases, these symptoms are most likely caused by your Magento admin session hitting Redis’s max_concurrency limit, especially if multiple admin tabs or background requests are involved.

What’s actually happening when you use multiple tabs

Magento stores your admin session in Redis. Redis enforces a rule that only a certain number of requests can “touch” your session at the same time. This is controlled by: max_concurrency (default = 6)
Here is what happens from your perspective:
  1. You open several admin tabs.
  2. Each tab loads data, makes background AJAX calls, or triggers an extension.
  3. Redis allows up to 6 simultaneous requests to write to your session. 
  4. The moment a 7th request tries to access the session, Redis blocks it.
  5. Magento cannot continue → it throws an exception → you see a backend error.
This explains why:
  • Only some tabs break while others work
  • Extensions fail even though nothing is wrong with them
  • Errors disappear if you close tabs or pause what you're doing
It is not caused by WriteText.ai specifically — any AJAX-heavy extension or multi-tab workflow can hit this limit.

How do I fix this permanently?

To stop these errors from happening again, you need to increase the Redis session concurrency limit in your Magento configuration. There is no single correct value for all stores. The right number depends on:
  • Your server or cluster capacity
  • How many admin users you have
  • How many admin tabs are typically open at the same time
  • How many background/AJAX requests your extensions make
  • Overall system concurrency limits
Your system administrator should choose a value that your environment can handle without causing performance issues.
  1. Open the file app/etc/env.php
  2. Find the session → redis section and change (or add) the max_concurrency value as appropriate to your environment:
 'session' => [
    'save' => 'redis',
    'redis' => [
        'host' => '127.0.0.1',
        'port' => '6379',
        'password' => '',
        'timeout' => '5',
        'persistent_identifier' => '',
        'database' => '2',
        'compression_threshold' => '2048',
        'compression_library' => 'gzip',
        'log_level' => '3',
        'max_concurrency' => '50',           // ← THIS IS THE FIX
        'break_after_frontend' => '5',
        'break_after_adminhtml' => '30',
        'first_lifetime' => '600',
        'bot_first_lifetime' => '60',
        'bot_lifetime' => '7200',
        'disable_locking' => '0',
        'min_lifetime' => '60',
        'max_lifetime' => '2592000'
    ]
],

 

Why increase the limit?

  • It allows Magento to handle multiple admin tabs without crashing
  • It supports modern extensions that use background requests
  • It reduces errors during testing, bulk actions, or heavy admin usage
Once updated, this issue typically disappears completely.
CONTENTS