[Next.js] Frontend Performance Issue After Adding Sentry

[dalnoki]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/browser

SDK Version

9.33

Framework Version

Next.js v15.3.2

Link to Sentry event

No response

Reproduction Example/SDK Setup

Additional details here.

Steps to Reproduce

After integrating Sentry’s Next.js They into their frontend, a customer experienced that their /login route response time increased from ~2 s to ~13 s. We are currently sending a small percentage of transactions (via tracesSampleRate: 0.05) and have Session Replay enabled. They confirmed that the slowness issue goes away when Sentry is disabled.

Expected Result

Minimal performance degradation

Actual Result

The load time is significantly higher than before adding Sentry

[mydea]

Can they test if the overhead remains if they remove session replay? I cannot imagine our SDK adding such a drastic overhead. How do they measure the response time?

[nagarajomnibound]

We have not enabled Session Replay in our Sentry setup.
We measured the response time using Chrome DevTools (Network tab), observing the login API taking ~13s with Sentry enabled vs ~2s without Sentry.

[chargome]

observing the login API taking ~13s with Sentry enabled vs ~2s without Sentry

Is this an API call to a /login route handler? Or a /login route (e.g. in your app router).

[nagarajomnibound]

It is a /login route in our app router, using Clerk third-party authentication for user login.