I have recently run into two file-upload glitches that were both one-offs in my 1 1/2 yr experience of similar uploads with Version 3.15.8+190130 on PHP 7.2. I am wondering if anyone else has experienced anything similar or has any suspicions of what might have gone on in these instances:
1. The first one-off was a respondent who submitted 5 files. The database recorded all 5 files, however the 2nd file was not present on the server even though it was saved in the response as though it had been successfully uploaded, complete with a dead link. The database record the missing filename as fu_... , so in this case something happened after the futmp_... was changed to fu_.... .
2. The second one-off was a different respondent who submitted 5 files on a different survey. The database recorded all 5 files, however the 1st file was not present on the server even though it was saved in the response as though it had been succesfully uploaded, complete with a dead link. This time the database record the missing filename as futmp_... , so in this case something happened before the futmp_... was changed to fu_.... . I did look in the tmp folder around 18 hours after the submission, but the temporary file was not there.
I have attempted to replicate this, though have not yet been successful in doing so. Both limesurvey and php are in process of being updated soon on this server, though I'm not sure that would have had an impact on these items. I am wondering if anyone taking the time to look at this has any thoughts or insights into what might be going on here, or if anyone has experienced something similar.
Last week we experienced a similar behaviour to what you describe in point no. 2 with version 3.22.4+200212: someone uploaded 10 files in total, but the first five failed and where stored as futmp_... in the database and could not be found on the server, the last five succeeded and where stored as fu_...
As of now we have no insights as to why that happened, but we are looking into it.
Uploaded files are temporarily stored as futmp_ until the respondent clicks on next, previous, resume later, or submit (depending on how a survey is configured). This is consistent with what happens if a user enters a response to a question but then exits (e.g., closes their browser tab) without any further action. In a such a case a temporary uploaded file would also not get saved with the survey. I think futmp_ files may also be wiped periodically, but in instances where the files are caught in time then there is a way to recover the files.
There used to be a similar issue if a user didn't click on "save changes" on the bottom-right after they uploaded, rather clicked on the x to close the box or clicked elsewhere on the page, but I think that may now be addressed.
Also, there can be issues if a respondent is uploading more than one large file and they progress to the next file before letting the current file finish uploading.
All of the above scenarios are things that can be reproduced to confirm what results in your version/environment.
(As to the one-off behavior that I experienced above, it was likely a cloud-server infrastructure related issue. PHP was upgraded shortly thereafter, which switched servers. It has not recurred since then.)
