Claude Troubleshooting: Attachment Upload Failures, Missing History, and Unavailable Models

When you encounter a Claude error, don’t rush to reinstall or keep refreshing—most issues can be located with a few troubleshooting steps. This article covers three common scenarios—“attachment upload failure,” “missing history,” and “model unavailable”—and provides the most reliable troubleshooting path for Claude on the web. Follow along, and in most cases you can get back to normal within ten minutes.

Claude Attachment Upload Failure: Check the File First, Then the Browser

The most common cause of Claude attachment upload failures is that the file itself is incompatible or too large. Prioritize converting the file to a more widely supported format (such as PDF, PNG, or TXT), and try again after compressing it appropriately. If it’s a scanned document, it’s recommended to convert it to searchable text or lower the resolution first—this can significantly reduce the chance of Claude getting stuck during upload.

If the file is fine, move on to the browser part of Claude troubleshooting: disable ad blockers, script plugins, and privacy-related extensions, then retry in an incognito window. If it still fails, clear the site cache and cookies, and switch to a different browser engine (for example, from certain customized browsers to Chrome/Edge). This often directly resolves Claude attachment upload failures.

Claude History Missing: Confirm Account and Cookies First, Then Check Sync

If your Claude history is missing, the first step isn’t to look for a “restore” button—it’s to confirm you’re logged into the same account (especially if you mix email login and third-party login). Many people overlook this during Claude troubleshooting: it may look like the “history is gone,” but in reality you’ve switched to a different login entry point.

If the account is correct, check whether your browser is blocking third-party cookies or automatically clearing site data, which can cause the Claude conversation list not to sync. Add Claude to the allowlist, keep your network stable, and avoid frequently switching network exits; then refresh the page or log in again—this usually brings the Claude history back.

Claude Models Unavailable or Not Selectable: Distinguish Between Service Congestion and Account Permissions

When Claude shows a model as unavailable, the model button is grayed out, or you’re prompted to try again later, it’s usually due to service busyness or temporary congestion. During Claude troubleshooting, you can first start a new chat, shorten the length of a single input, and reduce pasting extremely long content all at once, then try sending again—your success rate will be higher.

If it remains unavailable, confirm whether you’re within the correct subscription/permission scope and whether you’ve triggered a usage-limit notice. It’s also recommended to check Claude’s official status page (if available) for anomalies. If the status is normal but it’s still unavailable, log out and back in, or switch to a clean browser environment to rule out local-environment causes of Claude model unavailability.

Claude Message Send Failure and Endless Spinning: Use the “Network–Permissions–Content” Three-Step Method

When Claude fails to send, troubleshoot in order: first rule out network jitter (switch to a more stable network and avoid frequently changing IPs in a short time), then check permissions and login status (whether you’ve been disconnected or asked to re-verify). Often the problem isn’t the input content itself, but the session connection being interrupted midway.

If both network and login are normal, then check whether the content triggers blocking: split sensitive terms, long links, or large blocks of code into separate messages, or describe it in summary form first and then add details section by section. If it still fails repeatedly after the above steps, it’s recommended to compile an error screenshot, the timestamp, and reproduction steps, and submit them through Claude’s official feedback channel—this is more effective than blindly refreshing.