Hi Peter,
exactly, that is the issue.
And also 3 blocks imported from the bagpack are missing.
This is the full code now that the project is opened in the browser.
If i Save and close the project, it gives me the issue deleting the code and the blocks.
Even https://unchive.kodular.io/ doesn't show your blocks.
I studied your aia a bit. It has a number of long strings in your textboxes. Below is one of them.
^FS^CI27 ^FO202,331^GB55,0,1^FS ^FO201,332^GB0,55,1^FS ^FO201,386^GB134,0,1^FS ^FT576,0^A0R,17,18^FB387,1,4,C^FH^CI28^FDPreparato da Gruppo Caravelle srl^FS^CI27 ^FT558,0^A0R,17,18^FB387,1,4,C^FH^CI28^FDVia Appia Nuova 210 Roma - Italia^FS^CI27 ^FT292,140^A0N,17,18^FB307,1,4,C^FH^CI28^FDValori nutrizionali per ^FS^CI27 ^FT292,156^A0N,17,18^FB307,1,4,C^FH^CI28^FD100g di prodotto^FS^CI27 ^FO340,162^GFA,45,84,28,:Z64:eJz7/x8EfjDgBuz/kcA/PAoZIUoeMAAAg+kaxw==:662E ^FO340,217^GB211,0,1^FS ^FO339,247^GB212,0,1^FS ^FO339,276^GB212,0,1^FS ^FO339,303^GB212,0,1^FS ^FO339,330^GB212,0,1^FS ^FO339,358^GB212,0,1^FS ^FT342,185^A0N,17,18^FH^CI28^FDEnergia^FS^CI27 ^FT342,239^A0N,17,18^FH^CI28^FDGrassi^FS^CI27 ^FT342,269^A0N,17,18^FH^CI28^FDdi cui Acidi Saturi^FS^CI27 ^FT342,297^A0N,17,18^FH^CI28^FDCarboidrati^FS^CI27 ^FT342,323^A0N,17,18^FH^CI28^FDdi cui Zuccheri^FS^CI27 ^FT344,351^A0N,17,18^FH^CI28^FDProteine^FS^CI27 ^FT344,381^A0N,17,18^FH^CI28^FDSale^FS^CI27 ^BY1,3,40^FT386,52^BCN,,Y,N ^FH^FD>:03.03.500^FS ^FO483,165^GB0,221,1^FS ^FT497,269^A0N,17,18^FH^CI28^FD14.4g^FS^CI27 ^FT505,297^A0N,17,18^FH^CI28^FD1.2g^FS^CI27 ^FT505,323^A0N,17,18^FH^CI28^FD0.4g^FS^CI27 ^FT497,351^A0N,17,18^FH^CI28^FD29.4g^FS^CI27 ^FT497,378^A0N,17,18^FH^CI28^FD1.72g^FS^CI27 ^FT497,239^A0N,17,18^FH^CI28^FD29.2g^FS^CI27 ^PQ1,0,1,Y ^XZ
I don't know if this could cause that behavior when importing the aia or pasting blocks from the backpack.
I think I will assign one of the developers to this question.
When I put the string in a textbox I am able to copy and paste it from the backpack. Even importing the aia is working.
Hi Peter,
I was also afraid it was a matter of text field
So a workaround solution could be using "text box" instead of text field?
David
text box and text field are the same. 
App Inventors official name is "string block".
Good eyes. 
Just tested it. The character/escape code thingy is preventing the text box from being copied to the backpack.
Dear Peter,
IT SOLVED THE ISSUE
Anyway I created text box to be sure.
Then I removed the special character from the beggin.
After that i tryed to save and close.
After reopening that, it works.
I tryed aso to export aia and re import.
It works also!!!
The character was part of the zpl label. Anyway after deleting it it is still working.
Thank you very much for your time and great support !!!
David
@Juan_Antonio found the solution. Still like to know what "character" caused the problem. This is something that shouldn't happen.
ascii 197 = ┼
ascii197hereCT~~CD,~CC^~CT~ ^XA ~TA000 ~
I tested DLE and that wasn't it.
But I also think it should be one of the C0 controls.
It's 16 = DLE, but when you copy paste
" Click to copy and paste symbol" is converted to: 238 128 144
Again good catch.
The data link escape character (DLE) was intended to be a signal to the other end of a data link that the following character is a control character such as STX or ETX.
Furthermore, what is data link escape? data link escape - Computer Definition A communications control character that indicates that the following character is not data, but a control code.
It's a Byte Order Mark isn't it?
Had to search that also 
The byte order mark (BOM ) is a particular usage of the special Unicode character, U+FEFF BYTE ORDER MARK, whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text:[1]
@David_S 's app is interesting because it manages to send control characters to a Zebra Bluetooth printer.
