try again a lighter setup

no achordion

common/config.h

@@ -35,5 +35,5 @@
 // Enable rapid switch from tap to hold, disables double tap hold auto-repeat.
 #define QUICK_TAP_TERM 0
 
-// try to be more permissive with holds
-#define PERMISSIVE_HOLD
+// allow that thumb buttons have permissive hold
+#define PERMISSIVE_HOLD_PER_KEY

common/keymap.h

@@ -71,30 +71,16 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 
 };
 
-//
-// improve home row modifiers via achordion
-//
-
-#include "achordion.h"
-
-bool process_record_user(uint16_t keycode, keyrecord_t* record)
-{
-    if (!process_achordion(keycode, record)) {
-        return false;
+bool get_permissive_hold(uint16_t keycode, keyrecord_t *record) {
+    switch (keycode) {
+        case LT(_SYM, KC_SCLN):
+        case LT(_NUM, KC_SPC):
+        case LT(_NAV, KC_E):
+        case LT(_FN, KC_MINS):
+            // Immediately select the hold action when another key is tapped.
+            return true;
+        default:
+            // Do not select the hold action when another key is tapped.
+            return false;
     }
-
-    return true;
-}
-
-void matrix_scan_user(void)
-{
-    achordion_task();
-}
-
-bool achordion_chord(uint16_t tap_hold_keycode,
-                     keyrecord_t* tap_hold_record,
-                     uint16_t other_keycode,
-                     keyrecord_t* other_record)
-{
-    return my_on_left_hand(tap_hold_record->event.key) != my_on_left_hand(other_record->event.key);
 }

ferris/keymap.c

@@ -16,11 +16,5 @@
 
 #include QMK_KEYBOARD_H
 
-// split keyboard
-static bool my_on_left_hand(keypos_t pos)
-{
-    return pos.row < MATRIX_ROWS / 2;
-}
-
 // our shared 34 keys keymap
 #include "../common/keymap.h"

ferris/rules.mk

@@ -14,9 +14,6 @@ SPACE_CADET_ENABLE = no
 GRAVE_ESC_ENABLE = no
 MAGIC_ENABLE = no
 
-# add achordion to improve home row modifiers
-SRC += ../common/achordion.c
-
 # build
 # qmk compile -kb ferris/sweep -km christoph-cullmann
 # qmk flash -kb ferris/sweep -km christoph-cullmann