multiline grep search into separate files per occurence

I have a file as following: ***example.txt***

-1
    15
         1         0         0        11 -1.0000E+001  1.0000E+001 -1.0000E+001
         2         0         0        11  1.0000E+001  1.0000E+001 -1.0000E+001
...
        29         0         0        11  1.0000E+001  2.0000E+001  1.0000E+001
        30         0         0        11  5.0000E+000  5.0000E+000  5.0000E+000
    -1
 
#ffafsda
    -1
    780
         1       116         1         2         1         1         7        20
         1        11         2        15         4        18         3        12
        13        16        22        19         5        24         9        29
         8        27         6        23
    -1
	
	asfasd
	
	afsdasdf

It consists of blocks always starting and ending by line entirely matching ^ {4}-1$. I need to separate a file into multiple by these blocks. What I figured out right now is this multiline regex that extracts these blocks: grep -Pzo '(?s)((?m:^)\s{4}-1(?m:$).*?(?m:^)\s{4}-1(?m:$))' example.txt output:

-1
    15
         1         0         0        11 -1.0000E+001  1.0000E+001 -1.0000E+001
         2         0         0        11  1.0000E+001  1.0000E+001 -1.0000E+001
...
        29         0         0        11  1.0000E+001  2.0000E+001  1.0000E+001
        30         0         0        11  5.0000E+000  5.0000E+000  5.0000E+000
    -1    -1
    780
         1       116         1         2         1         1         7        20
         1        11         2        15         4        18         3        12
        13        16        22        19         5        24         9        29
         8        27         6        23
    -1

You see second match is exactly printed behind first match (no newline or separator) - I'm failing to separate these occurences into files required output is following: ***file1:***

-1
    15
         1         0         0        11 -1.0000E+001  1.0000E+001 -1.0000E+001
         2         0         0        11  1.0000E+001  1.0000E+001 -1.0000E+001
...
        29         0         0        11  1.0000E+001  2.0000E+001  1.0000E+001
        30         0         0        11  5.0000E+000  5.0000E+000  5.0000E+000
    -1

***file2***

-1
    780
         1       116         1         2         1         1         7        20
         1        11         2        15         4        18         3        12
        13        16        22        19         5        24         9        29
         8        27         6        23
    -1

Any help appreciated.