Hi,
That “response is not a valid JSON response” error means something on the server is interfering with the AJAX request WordPress uses to save widgets — it’s not specific to GeneratePress. A few things to check, in order:
1. Rule out a plugin/theme conflict
Temporarily switch to a default theme (e.g. Twenty Twenty-Four) and see if the error persists. If it does, it’s not the theme. Then deactivate all plugins and re-test; reactivate one at a time to find the culprit. Security, caching, and firewall plugins are the usual suspects.
2. Check the WordPress Site Health screen
Go to Tools → Site Health. This often flags the underlying cause directly — a REST API failure, a loopback request that can’t complete, or a PHP error.
3. Server-side causes (most common)
This error typically comes from the server, not WordPress:
- ModSecurity / WAF rules blocking the admin-ajax or REST request. Ask your host to check the ModSecurity logs for blocked requests around the time you saved.
- PHP error/timeout — check your server’s PHP error log for a fatal error firing during the save.
- Incorrect WordPress Address / Site Address URLs (Settings → General), especially a http/https or www mismatch.
- A security plugin (Wordfence, etc.) blocking the REST API.
4. Clear caching
If you use a caching plugin or a server/CDN cache (e.g. Cloudflare), clear it and retry.
The plugin-conflict test in step 1 plus the server logs in step 3 will usually pinpoint it. If you can share what your Site Health screen reports and whether disabling plugins resolves it, we can narrow it down further.
