主要就是OS 12.1 Beta 2 引入的问题，只要 UITabBar 是磨砂的，并且 push viewController 时 hidesBottomBarWhenPushed = YES 则手势返回的时候就会触发。解决方法如下，在项目中添加一个UIView分类，在.m文件里设置好你的tabbar正确的尺寸，即可正常运行。
伸手党的快乐，拿走
.h文件

import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIView (LLTabBarItem)

@end

NS_ASSUME_NONNULL_END

.m文件

import "UIView+LLTabBarItem.h"

import <objc/runtime.h>

@implementation UIView (CKTabBarItem)

• (void)load
  {
  if (@available(iOS 12.1, *)) {
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
  Class class = NSClassFromString(@"UITabBarButton");
  SEL originalSelector = @selector(setFrame:);
  SEL swizzledSelector = @selector(ck_setFrame:);
  Method originalMethod = class_getInstanceMethod(class, originalSelector);
  Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
  BOOL isSuccess = class_addMethod(class,
  originalSelector,
  method_getImplementation(swizzledMethod),
  method_getTypeEncoding(swizzledMethod));
  if (isSuccess) {
  class_replaceMethod(class,
  swizzledSelector,
  method_getImplementation(originalMethod),
  method_getTypeEncoding(originalMethod));
  } else {
  method_exchangeImplementations(originalMethod, swizzledMethod);
  }
  });
  }
  }

• (void)ck_setFrame:(CGRect)frame
  {
  if (!CGRectIsEmpty(self.frame)) {
  if (CGRectIsEmpty(frame)) {
  return;
  }
  frame.size.height = MAX(frame.size.height, 60.0);
  }
  [self ck_setFrame: frame];
  }

@end