The issue happened to be two-fold.
The table map event was recorded into binlog having
an incorrect size when number of columns exceeded 251. 
The Row-based event had incorrect recording and restoring m_width member within
the same as above conditions.

Fixed with correcting m_data_size and m_width.


mysql-test/suite/rpl/r/rpl_row_wide_table.result:
  the new test results.
mysql-test/suite/rpl/t/rpl_row_wide_table.test:
  regression test for bug#42977.
sql/log_event.cc:
  0. all buffers that used in net_store_length() are augmented with 1 for safety
  to be able to contain the magic and the content of ulonglong as well;
  1. Rows_log_event::get_data_size() yieled incorrect size |m_width/8| whereas 
     it should be m_width;
  2. Table_map_log_event::Table_map_log_event yieled incorrect value for
     `m_data_size' probably presuming 1-byte integer max for the column number;
sql/rpl_utility.h:
  DBUG_PRINT_BITSET() macro is left 256-cols limited but has made safe and commented.