Please help us help you and fill where relevant:
LimeSurvey version: LimeSurvey Community Edition   Version 6.15.2+250628 
Own server or LimeSurvey Cloud: Own server (shared provider VentraIP)
Survey theme/template: fruity
==================

I have been using LimeSurvey without trouble for the last year and a half on a shared hosting platform. For some reason, I am now unable to add participants or send invites. I get a blue spinner when I click on "new participant" or "send email invitation". 

I used ComfortUpdate just now and the issue persists with the updated version.

I copied the previously working survey to a new survey and I am able to add batch dummy participants but I can't make a new participant in the new survey - blue spinner.

Any troubleshooting ideas or tips?

I've been using LimeSurvey for almost 10 years and haven't had this particular problem.

 

Update on this one - I tried installing a new copy of LimeSurvey on a new subdomain. It's all set up. I created a new test survey and it still can't add participants.

I've tried
1. two different browsers (safari and chrome)
2. Incognito/private modes
3. clearing browsing data

This feels like there is some problem on my end but I can't figure it out. Any suggestions?

This sounds weird. Usually shared hostings have their limitations, but adding a single user shouldn't be a problem, even for a shared hosting environment. If it would be a huge CSV file with a lot of participants I could see an issue with a shared hoster.

I imported your LSS file and what I noticed is that your questions seem to be in the wrong order.

Just as a heads up.

I added a new participant through the participant section by clicking on "+ Add..." - "Add participant". I had no problem creating a new participant on LS 6.15.2+250628.

No "blue spinner". What makes me wonder is this "blue". I am not aware of any blue elements in the admin theme.

Could you show a screenshot of this blue spinner? I don't recognize this.

Thanks for the response. I just got a response from the hosting provider.

"When using the credentials provided and attempting to create a new participant, we can see the following error within the Dev Console

Failed to load resource: the server responded with a status of 503 ()
"

They are asking if there are more logs that might shed more light on this. Any suggestions?

I think the spinner is an OS thing. On iOS I get a grey screen. On windows I get a blue spinner with a hole in the middle. Regardless, it seems it's a 503 holding things up.

Interestingly, I just got a notification that the database had been updated from 623 to 630 and I can open the add participant page now. This happened after I changed the logging preferences in the config.php file to

'config'=>array(
'debug'=>2,
'debugsql'=>1,

Not sure if these things are related or not. On the interface there is a lot of debugging information so I can't use that for surveys.

But, when I change debug and debugsql back to zero (0), I can't create a new participant.

I changed to debug = 1 and it works again. Not so much information on the interface which is good.

Any suggestions?  Also, where do the logs go for debugging information on debug level 1?

Afaik 503 is a server error, so the logs would need to be on the servers side, not on LS side, in my opinion. But not an expert on server administration.

developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Status/503

Common causes are that a server is down for maintenance or overloaded. During maintenance, server administrators may temporarily route all traffic to a 503 page, or this may happen automatically during software updates.

So I don't see how this could be on LS side.

Yes, it seems like a 503 is a server side problem. The provider tells me there is nothing on their side that looks like a service is overloaded. They're asking about application logs to investigate further.

I have done a completely fresh install of 6.15 and can reproduce the error. I tried a downgrade to 6.10 and the problem continues. The strange thing is that when I increase debugging information using the debug setting in the config.php file, the problem goes away.

Something isn't happy in the system but I can't work out what it is.

How should I track down the issue? Where can I find logs?

As you can reproduce this in the latest version and in a previous version of Limesurvey and it goes away when debug mode on, I recommend to open a bug report under bugs.limesurvey.org.

Be as detailed as possible with your description there.

Ideally, post a link to your bug report here, so we can follow the progress.

Thanks holch.

bugs.limesurvey.org/view.php?id=20158

The hosting provider is looking into it because they were able to reproduce the issue. Suspect the problem is theirs but I can't see why changing debug settings would fix it.

They say that the 503 represents me hitting I/O limits but there isn't excessive traffic and it shouldn't be doing that.

Hosting provider found the issue. Here's a summary:

Root Cause Summary
The 503 errors during participant management operations (debug=0) were caused by incompatibility between LimeSurvey and Monarx (VentraIP's anti-virus/malware scanner). Specifically:

Silent Process Termination: When debug=0, PHP script failures triggered by Monarx caused LiteSpeed to return 503 errors ("Service Unavailable").
Debug Mode Masking: With debug=1/2, errors were displayed visibly instead of terminating silently, avoiding 503s.
No Resource Issue: Server-level checks confirmed no memory/CPU/disk constraints (confirmed via LVE limit tests).
Resolution Path
Immediate Fix: Disabling the Monarxprotect PHP module restored functionality.
Permanent Solution: VentraIP infrastructure team is rolling back the problematic Monarx update.
Workaround: Users can manually disable Monarx via "Select PHP Version" in hosting control panel if needed.
Key Technical Insight
"Monarx interfered with PHP process handling, causing silent termination (triggering LiteSpeed 503) when debug mode hid errors. Resource increases (memory/IO limits) couldn't resolve this application-layer conflict."

Thanks for the input.

I've copied this to bugs.limesurvey.com

Great that this could be solved.

Seems like your hosting provider is a good one and has put some effort into this. I don't think that is "normal".

Thank you for the feedback here, always good to know what happened (also for us to give feedback even if just guesses or examples of other cases, so that other might be able to search at the right place).