R help - May 2025 - Very odd issue getting "Input/output error" running shiny app from index.html locally but same shiny on my server working fine

I realise that shiny and Rstudio is often seen as OT here but I have a 
strong suspicion that the issue is R or R/OS related so I hope someone 
here will have some thoughts that might help me.

The scenario is that as of yesterday running my shiny project locally 
from within Rtudio, i.e. by opening the index.html with preview, gets me 
"Input/output error" when I click on a link to an app.

The same shiny running on my server (https://shiny.psyctc.org) runs 
fine. So if I click on the link 
https://shiny.psyctc.org/apps/COREpapers1 there then that app runs 
fine.? However, when I do the same locally I get "Input/output error"
in
the window that pops up where the app should run! Very bizarrely, if I 
open the app itself locally in Rstudio it runs fine.

I am completely baffled by this, have never seen it before and some 
searching on the web only suggest that "Input/output error" may be an
OS
level error and a suggestion that dmesg may give me a clue about it. 
However,dmesg is showing nothing that looks remotely pertinent and 
nothing new appears in rerunning dmesg immediately after invoking that 
error message.? I have updated and rebooted the local machine (rather 
desperate I admit) and that did update quite a lot of core linux files 
(despite my having updated this morning say six hours ago) ... but 
nothing new in R or R packages and the problem stayed the same.

To make it even more confusing the server and the local machine are both 
running R 4.5.0 (2025-04-11) and shiny version is 1.10.0 on both. I use 
git to package the server project and that gets transferred to the 
server from the local machine and commit is showing no local changes and 
the last change is showing as on 5.v.25.? The project can be seen at 
https://github.com/cpsyctc/shiny-server.

The server is running
 ?? Debian 5.10.197-1 (2023-09-29) x86_64 GNU/Linux
but the local machine runs
 ?? Linux tuxedo-os 6.11.0-114025-tuxedo #25~24.04.1tux1 SMP PREEMPT_DYNAMIC

I would hugely appreciate it if anyone has any thoughts about this, any 
things I might do to debug it more. It's currently getting in the way of 
some mildly urgent work I need to do on the server (of course it is, IT 
knows when you are vulnerable!)

TIA,

Chris

-- 
Chris Evans (he/him)
Visiting Professor, UDLA, Quito, Ecuador
CORE site: http://www.coresystemtrust.org.uk 
<https://www.coresystemtrust.org.uk/>
Other work web site: https://www.psyctc.org/psyctc/
Personal site: https://www.psyctc.org/pelerinage2016/
<https://ombook.psyctc.org/book>