gawk 4.0.2 issue - "fatal: not enough arguments to satisfy format string"

[Zhu, John (Nokia - CN/Shanghai)]

Hello Developers,

My name is John Zhu and I am a software engineer in Nokia China.

I found an issue with gawk 4.0.2 on my RHEL 7.6 VM, please help to check if 
it's a potential bug.

I have two text files a and b with only one byte different.
The last character of the second line in file a is letter "o" in lower case 
while in the same location in file b is letter "A" in upper case.
[root@betactvdh:/tmp]# cat a
1
2% o
3
4
5
6
[root@betactvdh:/tmp]# cat b
1
2% A
3
4
5
6
[root@betactvdh:/tmp]# diff a b
2c2
< 2% o
---
> 2% A
[root@betactvdh:/tmp]# hexdump -C a
00000000  31 0a 32 25 20 6f 0a 33  0a 34 0a 35 0a 36 0a     |1.2% o.3.4.5.6.|
0000000f
[root@betactvdh:/tmp]# hexdump -C b
00000000  31 0a 32 25 20 41 0a 33  0a 34 0a 35 0a 36 0a     |1.2% A.3.4.5.6.|
0000000f
[root@betactvdh:/tmp]#
[A close up of a screen  Description automatically generated]
Awk version is GNU Awk 4.0.2.
[root@betactvdh:/tmp]# awk --version
GNU Awk 4.0.2
Copyright (C) 1989, 1991-2012 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
[root@betactvdh:/tmp]#

I run the same command to folder the six line text into two lines.
It works with file b:
[root@betactvdh:/tmp]# cat b|awk 
'{for(i>0;i<=NR;i++)a[i]=$0}END{for(j=0;3*j+1<i;j++){printf"|";for(k=1;k<=3;k++)printf
 a[3*j+k]"|";printf"\n"}}'
|1|2% A|3|
|4|5|6|

But it doesn't work with file a:
[root@betactvdh:/tmp]# cat a|awk 
'{for(i>0;i<=NR;i++)a[i]=$0}END{for(j=0;3*j+1<i;j++){printf"|";for(k=1;k<=3;k++)printf
 a[3*j+k]"|";printf"\n"}}'
|1|awk: cmd. line:1: (FILENAME=- FNR=6) fatal: not enough arguments to satisfy 
format string
        `2% o|'
           ^ ran out for this one

[A screenshot of a cell phone  Description automatically generated]
I also tested on other awk releases and found same issue on GNU Awk 3.1.7 as 
well.
[cid:image003.png@01D5F5D6.0066C800]

Please advise why it is happening.

Thanks & Regards,
John