what is the strangest bug you found

What is the strangest bug you found?
I remember once I found very strange bug and it was like this.
I was testing Email functionality. 
We have internal email client inside the application and 
I was sending email with attachements.
For some reason certain type of attachements couldn't open when email was
send in the morning. Very strange! Really strange issue. So in afternoon
everything was fine but if you open the attachment it in the morning it was
giving 401 unauthorized error. So you are trying click on excel file that was
send over the email as an attachment but instead opening file it was giving
an error. Very strange. So what developers did they run the application
locally we look into that together and they just connect it to the test 
enviroment database to the same enviroment So they could see same data 
same user everything. And also we were looking into this server where 
documents stored. So what actually happens when you send attachment or 
any kind of file what application does it stores that file in the server aswell.
but the adress of the file will be encrypted. but in the server we were
able to see those files nothing has changed but when receipent of the email
trys to open it his getting error. We were looking into server logs to
investigate this error and couldn't understand what happened. So it wasn't 
the bug yet because nobody could understand where is the problem,
it's a kind of problem but to determine we need to find out
where is the root cause  of this problem. To determine it's a bug indeed. 
And solution was even stranger we just re-deployed application
that is responsible for this files hosting. So it was seperate that is
 managing access to files. And simple re-deployment solved this issue.
Developers spent whole day on trying to figure out what was the problem
and investigate everything after re-deployment there was even no code change 
everything was the same but refreshing solve the problem. It was the strangest
issue I have ever seen

I remember once I found very strange bug and it was like this.
I was testing Email functionality.
We have internal email client inside the application and
I was sending email with attachements.
For some reason certain type of attachements couldn't open when email was
send in the morning. Very strange! Really strange issue. So in afternoon
everything was fine but if you open the attachment it in the morning it was
giving 401 unauthorized error. So you are trying click on excel file that was
send over the email as an attachment but instead opening file it was giving
an error. Very strange. So what developers did they run the application
locally we look into that together and they just connect it to the test
enviroment database to the same enviroment So they could see same data
same user everything. And also we were looking into this server where
documents stored. So what actually happens when you send attachment or
any kind of file what application does it stores that file in the server aswell.
but the adress of the file will be encrypted. but in the server we were
able to see those files nothing has changed but when receipent of the email
trys to open it his getting error. We were looking into server logs to
investigate this error and couldn't understand what happened. So it wasn't
the bug yet because nobody could understand where is the problem,
it's a kind of problem but to determine we need to find out
where is the root cause  of this problem. To determine it's a bug indeed.
And solution was even stranger we just re-deployed application
that is responsible for this files hosting. So it was seperate that is
 managing access to files. And simple re-deployment solved this issue.
Developers spent whole day on trying to figure out what was the problem
and investigate everything after re-deployment there was even no code change
everything was the same but refreshing solve the problem. It was the strangest
issue I have ever seen