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Dashboard disconnecting when Chart node is used #2318
Description
Current Behavior
version 1.33
I use version 1.33.0. Problem occurs after data arrive in chart. Interval for data is 5 seconds. I need to store data 24 hours but problem occurs even after 10 seconds from start.
snipet of browser console log
Violation] Added non-passive event listener to a scroll-blocking 'mousewheel' event. Consider marking event handler as 'passive' to make the page more responsive. See https://www.chromestatus.com/feature/5745543795965952
Expected Behavior
No response
Steps To Reproduce
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Environment
- Dashboard version:
- Node-RED version:
- Node.js version:
- npm version:
- Platform/OS:
- Browser:
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n-lark commentedon Oct 19, 2026
Thanks for logging this @hardillb
I looked at this and from details provided isn't clear what's wrong. The
mousewheelviolation is a Chrome performance hint, not an error, and nothing in the flow stands out to me. To take this forward we'd need more details like is the page freezing, is the chart not updating, or something else?ristabr commentedon Oct 20, 2026
Hello. This is issue I posted in chat bot on flow fuse page.
I will provide more details about this problem.
Thank you for your response.
ristabr commentedon Oct 20, 2026
I have issue with constant disconnecting from server when I open dashboard page where is ui-chart control shown. Data for chart is polled from Modbus device every 5 seconds. Chart is configured to show data for last 24 hours.
Everything was working normally until I updated Node-Red and also Dashboard couple of days ago.
From update, when I open chart page first time, it is working normally. When I switch to other page and then go back to chart, page becomes frozen and message for disconnection from server is flickering in the upper right corner.
If I switch to other page, connection is restored but as soon as I go to chart page, connection is lost again.
I tried to lower period for data on the chart to 1 hour, 1 minute, even to 10 points but problem stays.
When I disable only chart control on the page, page is working normally so clearly problem is with chart control somehow.
I checked with ui-control node and debug node for connection status, and I get 2 or 3 times per second message about connection loss while page with ui-chart node is shown.
My server is running on Windows system PC, and dashboard is opened on another PC in Microsoft Edge browser.
Even when I open page on the same PC where the server is running, I have same problem.
Node-Red version is: 5.0.8
Dashboard version is: flowfuse/node-red-dashboard 1.33.0
n-lark commentedon Oct 20, 2026
Hey I was able to reproduce this on Dashboard 1.33.0 with Node-RED 5.0.8.
What's happening is the Modbus read node attaches a binary
Bufferto each messagemsg.responseBuffer.buffer. The chart stores the full message for every point, Buffer included. When the chart page opens, the dashboard sends that stored history to the browser in one go, with each Buffer as a separate binary attachment.Since 1.31.0, the dashboard's socket library limits a single message to 10 binary attachments. Once the chart holds more than 10 points, the browser rejects the history and drops the connection. It then reconnects, requests the history again, and the cycle repeats. That's the flickering "disconnected" message.
Workaround
A possible workaround for now is to remove the Buffer just before the chart like with a Change node set to Delete
msg.responseBuffer, wired between "Fixed decimal" and the chart.I'll look into a fix on our end, but that should get you back in action.
colinl commentedon Oct 20, 2026
@n-lark I have occasionally wondered whether it is necessary for the chart to save the complete message. I think it can always be determined from the chart config what data are required, though perhaps there are complications that I have not thought of.
n-lark commentedon Oct 20, 2026
Hey @colinl I wondered the same thing but was worried about complications as well since other things may depend on the full message. I went with removing the attachment limit on the client side instead which leaves the stored data unchanged PR is here #2323
colinl commentedon Oct 20, 2026
I wasn't suggesting this as a fix for this issue, more just logging the idea for later consideration.
ristabr commentedon Oct 20, 2026
I will test proposed workaround tomorrow when I am at work and inform you.
Hope this will fix problem.
Thank you.
ristabr commentedon Oct 21, 2026
Hello.
I just tested workaround as @n-lark proposed and now is ok. Everything works as before.
In change node, before splitting data array from Modbus poll, I added step to delete msg.responseBuffer.
Thank you very much for this.